Department of Kinesiology and Applied Physiology WCR

Human Anatomy and Physiology II KAAP310-15F

Lecture: Kirkbride 004, Tue, Thu 11:00-12:15

Course Web Site www.udel.edu/sakai

William Rose rosewc@udel.edu Rust 148

Department of Kinesiology and Applied Physiology WCR

Human Anatomy and Physiology II KAAP310-15F

Labs (HSC 228)020 Thu 12:30-2:25 (Jahyun Kim)021 Fri 8:00 – 9:55 (Jahyun Kim)022 Fri 10:10 – 12:05 (Jahyun Kim)023 Fri 12:20 – 2:15 (Joe Watso)

Run: Tuesdays 12:45-1:30, from CSB entrance, 1-2 miles relaxed pace.

Department of Kinesiology and Applied Physiology WCR

Human Anatomy and Physiology IIKAAP310-15F

Grading – see syllabus.

75% Classroom 70%: Ten tests (worst is dropped so nine count) 5%: Clicker

25% Laboratory

Department of Kinesiology and Applied Physiology WCR

Human Anatomy and Physiology IIKAAP310-15F

UD Capture: Recording of what is projected on screen and classroom audio. http://udcapture.udel.edu/2015s/kaap310-010/

Clickers: Register your clicker on Sakai.

Clicker questions: 1 point for answering, 1 more point if correct.

Clicker grade: Full credit if you get 75% or more of the points available. Reduced proportionally if not.

Using more than one clicker is academic dishonesty and may be referred to the Office of Syduent Conduct.

No adjustments for forgotten or broken clickers, low batteries, etc.

Human Anatomy and Physiology IIKAAP310-15F

Tips

This class is not the same as KAAP 309.

Do not rely on memorization.

Understanding physiology requires knowing more than the what or where. You need to understand the why and the how.

Human Anatomy and Physiology IIKAAP310-15F

TipsEveryone will work hard.Read the book, come to class, ask questions.Use the recorded lectures to review and not as

a substitute for coming to class. Use the online resources.

Exam Questions

KnowledgeComprehensionApplication

Knowledge Question________ are chemical messengers that are released in one tissue and transported in the bloodstream to alter the activities of specific cells in other tissues.

A.Hormones

B.Neuropeptides

C.Neurotransmitters

D.Humoral antibodies

E.none of the above

Comprehension QuestionAn activated G protein can trigger A.the opening of calcium ion

channels in the membrane.

B.the release of calcium ions from intracellular stores.

C.a fall in cAMP levels.

D.a rise in cAMP levels.

E.all of the above

Application QuestionDestruction of the supraoptic nucleus of the hypothalamus would have which result?

A.loss of emotional response B.loss of GH secretion C.loss of ADH secretion D.loss of loss of regulatory factor secretionE.loss of melatonin secretion

Endocrine System: Overview

• Acts with the nervous system to coordinate and integrate the activity of body cells

• Influences metabolic activities by means of hormones transported in the blood

• Responses occur more slowly but tend to last longer than those of the nervous system

• Endocrinology

• Study of hormones and endocrine organs

• Controls and integrates

• Reproduction

• Growth and development

• Maintenance of electrolyte, water, and nutrient balance of blood

• Regulation of cellular metabolism and energy balance

• Mobilization of body defenses

Figure 16.1

Pineal glandHypothalamus

Pituitary gland

Parathyroid glands(on dorsal aspectof thyroid gland)Thymus

Thyroid gland

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

Other tissues and organs that produce hormones: adipose cells, thymus, cells in walls of the small intestine, stomach, kidneys, heart

Chemical Messengers

• Hormones: long-distance chemical signals that travel in the blood or lymph

• Autocrines: chemicals that exert effects on the same cells that secrete them

• Paracrines: locally acting chemicals that affect cells other than those that secrete them

• Autocrines and paracrines are local chemical messengers and will not be considered part of the endocrine system

Mechanisms of Hormone Action

• Hormone action on target cells may be to

• Alter plasma membrane permeability of membrane potential by opening or closing ion channels

• Stimulate synthesis of proteins or regulatory molecules

• Activate or deactivate enzyme systems

• Induce secretory activity

• Stimulate mitosis

Chemistry of Hormones

• Two main classes

1.Amino acid-based hormones

• Amino acid derivatives, peptides, and proteins

2.Steroids

• Synthesized from cholesterol

• Gonadal and adrenocortical hormones

1. Water-soluble hormones (all amino acid–based hormones except thyroid hormone)

• Two mechanisms, depending on their chemical nature

1. Water-soluble hormones (all amino acid–based hormones except thyroid hormone)

• Cannot enter the target cells

• Act on plasma membrane receptors

• Coupled by G proteins to intracellular second messengers that mediate the target cell’s response

Hormone (1st messenger)binds receptor.

Receptor

Extracellular fluid

Cytoplasm

G protein (GS)

Cannot enter the target cells. Act on plasma membrane receptors. Coupled by G proteins to intracellular second messengers that mediate the target cell’s response

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor that directly activates genes.

Plasmamembrane

2. Lipid-soluble hormones (steroid/thyroid hormones)

Figure 16.2

Hormone (1st messenger)binds receptor.

Receptoractivates Gprotein (GS).

G proteinactivatesadenylatecyclase.

cAMP acti-vates proteinkinases.

Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).

Receptor

G protein (GS)

Adenylate cyclase

Triggers responses oftarget cell (activatesenzymes, stimulatescellular secretion,opens ion channel,etc.)

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Inactiveprotein kinase

Extracellular fluid

Cytoplasm

Activeproteinkinase

GDP

GlucagonPTHTSHCalcitonin

1

2 3 4

5

Plasma Membrane Receptors and Second-Messenger Systems - cAMP

Plasma Membrane Receptors and Second-Messenger Systems

• cAMP signaling mechanism

• Activated kinases phosphorylate various proteins, activating some and inactivating others

• cAMP is rapidly degraded by the enzyme phosphodiesterase

• Intracellular enzymatic cascades have a huge amplification effect

Plasma Membrane Receptors and Second-Messenger Systems

• PIP2-calcium signaling mechanism

http://www.ruf.rice.edu/~rur/issue1_files/barron.html

•DAG activates protein kinases; IP3 triggers release of Ca2+

•Ca2+ alters enzymes or channels or binds to the regulatory protein calmodulin

PIP2 – phosphatidyl inositol bisphosphate

Other Signaling Mechanisms

• Cyclic guanosine monophosphate (cGMP) is second messenger for some hormones

• Some work without second messengers

• E.g., insulin receptor is tyrosine kinase enzyme that autophosphorylates upon insulin binding docking for relay proteins that trigger cell responses

Figure 16.3, step 5

mRNA

New protein

DNA

Hormoneresponseelements

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

The receptor-hormone complex entersthe nucleus.

The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).

Binding initiatestranscription of thegene to mRNA.

The mRNA directsprotein synthesis.

Plasmamembrane

1

2

3

4

5

Intracellular Receptors and Direct Gene Activation

Target Cell Specificity

• Target cells must have specific receptors to which the hormone binds

• ACTH receptors are only found on certain cells of the adrenal cortex

• Thyroxin receptors are found on nearly all cells of the body

Target Cell Activation

• Target cell activation depends on three factors

1. Blood levels of the hormone

2. Relative number of receptors on or in the target cell

3. Affinity of binding between receptor and hormone

• Hormones influence the number of their receptors

• Up-regulation—target cells form more receptors in response to the hormone

• Down-regulation—target cells lose receptors in response to the hormone

Hormones in the Blood

• Hormones circulate in the blood either free or bound

• Steroids and thyroid hormone are attached to plasma proteins

• All others circulate without carriers

• The concentration of a circulating hormone reflects:

• Rate of release

• Speed of inactivation and removal from the body

• Hormones are removed from the blood by

• Degrading enzymes

• Kidneys

• Liver

Half-life—the time required for a hormone’s blood level to decrease by half

Interaction of Hormones at Target Cells

• Multiple hormones may interact in several ways

• Permissiveness: one hormone cannot exert its effects without another hormone being present

• Synergism: more than one hormone produces the same effects on a target cell

• Antagonism: one or more hormones opposes the action of another hormone

• Permissiveness: one hormone cannot exert its effects without another hormone being present

• Synergism: more than one hormone produces the same effects on a target cell

• Antagonism: one or more hormones opposes the action of another hormone

Control of Hormone Release

• Blood levels of hormones

• Are controlled by negative feedback systems

• Vary only within a narrow desirable range

• Hormones are synthesized and released in response to

1. Humoral stimuli

2. Neural stimuli

3. Hormonal stimuli

Humoral Stimuli

• Changing blood levels of ions and nutrients directly stimulates secretion of hormones

• Examples:

Figure 16.4a

(a) Humoral Stimulus

Capillary (lowCa2+ in blood)

Parathyroidglands

Thyroid gland(posterior view)

PTH

Parathyroidglands

1 Capillary blood containslow concentration of Ca2+,which stimulates…

2 …secretion ofparathyroid hormone (PTH)by parathyroid glands*

•Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone)

•PTH causes Ca2+ concentrations to rise and the stimulus is removed

Humoral Stimuli

Figure 16.4b

(b) Neural Stimulus

CNS (spinal cord)

Medulla ofadrenalgland

Preganglionicsympatheticfibers

Capillary

1 Preganglionic sympatheticfibers stimulate adrenalmedulla cells…

2 …to secrete catechola-mines (epinephrine andnorepinephrine)

• Nerve fibers stimulate hormone release

• Sympathetic nervous system fibers stimulate the adrenal medulla to secrete catecholamines

Neural Stimuli

Figure 16.4c

(c) Hormonal Stimulus

Hypothalamus

Thyroidgland

Adrenalcortex

Gonad(Testis)

Pituitarygland

1 The hypothalamus secreteshormones that…

2 …stimulatethe anteriorpituitary glandto secretehormonesthat…

3 …stimulate other endocrineglands to secrete hormones

Hormonal Stimuli• Hormones stimulate other

endocrine organs to release their hormones

• Hypothalamic hormones stimulate the release of most anterior pituitary hormones

• Anterior pituitary hormones stimulate targets to secrete still more hormones

• Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from the final target organs inhibit the release of the anterior pituitary hormones

Nervous System Modulation

• The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms

• Example: under severe stress, the hypothalamus and the sympathetic nervous system are activated

• As a result, body glucose levels rise

The Pituitary Gland and Hypothalamus

• “Master gland”, hypophysis, 600 mg (!)

• In hypophyseal fossa, above sella turcica of sphenoid bone

• Posterior pituitary (neurohypophysis)

• Anterior pituitary (adenohypophysis)

Pituitary-Hypothalamic Relationships

• Posterior lobe (neurohypophysis)

• A downgrowth of hypothalamic neural tissue

• Neural connection to the hypothalamus (hypothalamic-hypophyseal tract)

• Nuclei of the hypothalamus synthesize the neurohormones oxytocin and antidiuretic hormone (ADH)

• Neurohormones are transported to the posterior pituitary

Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).

Oxytocin and ADH are stored in axon terminals in the posterior pituitary.

When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.

1

2

3

4OxytocinADH

Posterior lobeof pituitary

Opticchiasma

Infundibulum(connecting stalk)

Hypothalamic-hypophyseal

tract

Axon terminals

Posterior lobeof pituitary

Paraventricular nucleus

Hypothalamus

Supraopticnucleus

Inferiorhypophysealartery

Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.

Pituitary-Hypothalamic Relationships

• Anterior Lobe (adenohypophysis):

• Originates as an out-pocketing of the oral mucosa

• Hypophyseal portal system

• Primary capillary plexus

• Hypophyseal portal veins

• Secondary capillary plexus

• Carries releasing and inhibiting hormones to the anterior pituitary to regulate hormone secretion

Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary.

In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation.

GH, TSH, ACTH,FSH, LH, PRL

Anterior lobeof pituitary

When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.

Hypophysealportal system• Primary capillary plexus• Hypophyseal portal veins• Secondary capillary plexus

Superiorhypophyseal

artery

Anterior lobeof pituitary

Hypothalamus Hypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.

A portal system is two capillary plexuses (beds) connected by veins.

12

3

Anterior Pituitary Hormones

• Growth hormone (GH)

• Thyroid-stimulating hormone (TSH) or thyrotropin

• Adrenocorticotropic hormone (ACTH)

• Follicle-stimulating hormone (FSH)

• Luteinizing hormone (LH)

• Prolactin (PRL)

• All are proteins

• All except GH activate cyclic AMP second-messenger systems at their targets

• TSH, ACTH, FSH, and LH are all tropic hormones (regulate the secretory action of other endocrine glands)

Figure 16.6

Growth hormone

Feedback Inhibits GHRH releaseStimulates GHIHreleaseInhibits GH synthesisand release

Anteriorpituitary

Liver andother tissues

Indirect actions(growth-promoting)

Direct actions(metabolic,anti-insulin)

Insulin-like growthfactors (IGF-1)

ExtraskeletalSkeletal FatCarbohydratemetabolism

Increased cartilageformation and

skeletal growth

Increased proteinsynthesis, andcell growth and

proliferation

Increasedfat breakdown

and release

Increased bloodglucose and otheranti-insulin effects

EffectsEffects

Produce

Hypothalamussecretes growthhormone—releasinghormone (GHRH), andsomatostatin (GHIH)

Initial stimulus

Physiological response

Result

Increases, stimulates

Reduces, inhibits

•Stimulates most cells, but targets bone and skeletal muscle•Promotes protein synthesis and encourages use of fats for fuel•Most effects are mediated indirectly by insulin-like growth factors (especially IGF-1)

Growth Hormone (GH or Somatotropin)

Figure 16.6

Growth hormone

Feedback Inhibits GHRH releaseStimulates GHIHreleaseInhibits GH synthesisand release

Anteriorpituitary

Liver andother tissues

Indirect actions(growth-promoting)

Direct actions(metabolic,anti-insulin)

Insulin-like growthfactors (IGF-1)

ExtraskeletalSkeletal FatCarbohydratemetabolism

Increased cartilageformation and

skeletal growth

Increased proteinsynthesis, andcell growth and

proliferation

Increasedfat breakdown

and release

Increased bloodglucose and otheranti-insulin effects

EffectsEffects

Produce

Hypothalamussecretes growthhormone—releasinghormone (GHRH), andsomatostatin (GHIH)

Initial stimulus

Physiological response

Result

Increases, stimulates

Reduces, inhibits

GH release is regulated by

•Growth hormone–releasing hormone (GHRH)

•Growth hormone–inhibiting hormone (GHIH) (somatostatin)

Growth Hormone (GH or Somatotropin)

Homeostatic Imbalances of Growth Hormone

• Hypersecretion

• In children results in gigantism

• In adults results in acromegaly

• Hyposecretion

• In children results in pituitary dwarfism

Figure 16.7

Hypothalamus

Anterior pituitary

Thyroid gland

Thyroidhormones

TSH

TRH

Target cellsStimulates

Inhibits

Thyroid-Stimulating Hormone (Thyrotropin)

Regulation:

• Stimulated by thyrotropin-releasing hormone (TRH)

• Inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus

Figure 16.7

Hypothalamus

Anterior pituitary

Thyroid gland

Thyroidhormones

TSH

TRH

Target cellsStimulates

Inhibits

Thyroid-Stimulating Hormone (Thyrotropin)

• Produced by thyrotrophs of the anterior pituitary

• Stimulates the normal development and secretory activity of the thyroid

Adrenocorticotropic Hormone (Corticotropin)

• Secreted by corticotrophs of the anterior pituitary

• Stimulates the adrenal cortex to release corticosteroids

• Regulation of ACTH release

• Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm

• Internal and external factors such as fever, hypoglycemia, and stressors can alter the release of CRH

Gonadotropins

• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

• Secreted by gonadotrophs of the anterior pituitary

• FSH stimulates gamete (egg or sperm) production

• LH promotes production of gonadal hormones

• Absent from the blood in prepubertal boys and girls

• Regulation of gonadotropin release

• Triggered by the gonadotropin-releasing hormone (GnRH) during and after puberty

• Suppressed by gonadal hormones (feedback)

Prolactin (PRL)

• Secreted by lactotrophs of the anterior pituitary

• Stimulates milk production, slowly and long term

• Regulation of PRL release

• Primarily controlled by prolactin-inhibiting hormone (PIH) (now known to be dopamine)

• Blood levels rise toward the end of pregnancy

• Suckling stimulates PRH release and promotes continued milk production

Adapted from Fahlbusch R: Endocrinol Metab Clin 21:669, 1992. Fauci et al., Harrison's Principles of Internal Medicine, 17th ed. from www.accessmedicine.com.

Transsphenoidal resection of pituitary mass via the

endonasal approach.

“Hypogonadism Due to Pituicytoma in an Identical Twin”

H. H. Newnham & L. M. Rivera-Woll

New Engl J Med 359: 2824, 2008

See here.

The Posterior Pituitary

• Contains axons of hypothalamic neurons

• Stores antidiuretic hormone (ADH) and oxytocin

• ADH and oxytocin are released in response to nerve impulses

• Both use PIP-calcium second-messenger mechanism at their targets

Oxytocin

• Stimulates uterine contractions during childbirth

• Also triggers milk ejection (“letdown” reflex) in women producing milk

• Suckling stimulates oxytocin release: positive feedback loop, with infant completing the loop

• Acts as a neurotransmitter in brain: the love hormone

Antidiuretic Hormone (ADH)

• Hypothalamic osmoreceptors respond to changes in the solute concentration of the blood

• Other name: vasopressin

• If solute concentration is high

• Osmoreceptors depolarize and transmit impulses to hypothalamic neurons

• ADH is synthesized and released, inhibiting urine formation

Antidiuretic Hormone (ADH)

• ADH works at the kidney to control water loss

• If solute concentration is high (sensed by osmoreceptors in the hypothalamus)

• A large amount of ADH is released, inhibiting water loss

• If solute concentration is low

• ADH is not released, allowing water loss

• Alcohol inhibits ADH release and causes copious urine output

Homeostatic Imbalances of ADH

• ADH deficiency: diabetes insipidus. Huge output of urine and intense thirst

• ADH hypersecretion (after neurosurgery, trauma, or secreted by cancer cells)—syndrome of inappropriate ADH secretion (SIADH)

Case Study

History of Present Illness:

Lucia Sanchez is a 24 year-old woman who presented to her physician with a chief complaint of urinary frequency (polyuria) and excessive thirst (polydipsia). Her polyuria began abruptly two weeks prior to her doctor's appointment. Prior to that time, Lucia voided approximately five times per day. She estimated that she was now voiding twenty times per day. Two days prior to her visit to the doctor's office she was advised to collect her urine in order to check its volume in a 24 hour period; her total urine volume measured 12 liters. Lucia also noticed an intense craving for ice water that began at about the same time as her polyuria. If she did not have access to water, she would become extremely thirsty and dizzy. She denied any change in her appetite. She also denied the use of any medications.

Case Study

Case Study

Lucia was hospitalized and underwent an oral dehydration test. She was denied any fluid intake, and doctors carefully analyzed her vital signs and urine output during this process. Because she had been advised to drink a lot of water before coming to the hospital, her initial supine and upright blood pressure were normal. The analysis showed that Lucia was urinating at a rate of approximately 500 cc's per hour; her urine specific gravity remained at 1.001 even though she became dehydrated to the point where she became orthostatic (her blood pressure dropped when she changed from the supine to the upright position).

Case Study

Diagnosis: Central diabetes insipidus

Lucia was given ADH which resulted in a marked decline in her urine output from 500 cc/hour to 70 cc/hour. Nurses administered IV fluids to correct her dehydration. Lucia was discharged and instructed to take desmopressin acetate, an oral form of ADH. This will mimic her physiologic levels of ADH, and help her kidneys retain water.

An overview of the relationships between hypothalamic and pituitaryhormones, and some effects of pituitary hormones on target tissues

Hypothalamus

Indirect Control through Releaseof Regulatory Hormones

Direct Releaseof Hormones

Corticotropin-releasinghormone(CRH)

Thyrotropin-releasinghormone

(TRH)

Growthhormone-releasinghormone(GH-RH)

Growthhormone-inhibitinghormone(GH-IH)

Prolactin-releasing

factor(PRF)

Prolactin-inhibitinghormone

(PIH)

Gonadotropin-releasinghormone(GnRH)

Sensorystimulation

Osmoreceptorstimulation

Regulatory hormones are released intothe hypophyseal portal system for delivery

to the anterior lobe of thepituitary gland.

Posterior lobeof pituitary gland

Kidneys

Males: Smoothmuscle in ductusdeferens andprostate gland

Females: Uterinesmooth muscle andmammary glands

Melanocytes (uncertainsignificance in healthyadults)

Ovariesof femaleTestes

of maleMammaryglands

Bone, muscle,other tissues

Thyroidgland

Adrenalglands

Adrenal cortex Anterior lobe ofpituitary gland

ACTH

TSHGH

PRLFSH LH

MSH

OXT

ADH

Liver

Somatomedins

Glucocorticoids(steroid

hormones)

Thyroidhormones

Inhibin Testosterone Estrogen Progesterone Inhibin

Thyroid Gland

• Consists of two lateral lobes connected by a median mass called the isthmus

• Composed of follicles that produce the glycoprotein thyroglobulin

• Colloid (thyroglobulin + iodine) fills the lumen of the follicles and is the precursor of thyroid hormone

• Parafollicular cells produce the hormone calcitonin

Figure 16.8

Thyroid Hormone (TH)

• Actually two related compounds

• T4 (thyroxine); has 2 tyrosine molecules + 4 bound iodine atoms

• T3 (triiodothyronine); has 2 tyrosines + 3 bound iodine atoms

Affects virtually every cell in body

• Major metabolic hormone

• Increases metabolic rate and heat production (calorigenic effect)

• Plays a role in

• Regulation of tissue growth

• Development of skeletal and nervous systems

• Reproductive capabilities

Figure 16.9, step 7

To peripheral tissues

T3

T3

T3

T4

T4

Lysosome

Tyrosines (part of thyroglobulinmolecule)

T4

DIT (T2)Iodine

MIT (T1)

Thyro-globulincolloid

Iodide (I–)

RoughER

Capillary

Colloid

Colloid inlumen offollicle

Thyroid follicle cells

Iodinated tyrosines arelinked together to form T3

and T4.

Iodideis oxidizedto iodine.

Thyroglobulin colloid isendocytosed and combinedwith a lysosome.

Lysosomal enzymes cleaveT4 and T3 from thyroglobulincolloid and hormones diffuseinto bloodstream.

Iodide (I–) is trapped(actively transported in).

Thyroglobulin is synthesized anddischarged into the follicle lumen.

Iodine is attached to tyrosinein colloid, forming DIT and MIT.

Golgiapparatus

1

2

3

4

5

6

7

Transport and Regulation of TH

• T4 and T3 are transported by thyroxine-binding globulins (TBGs)

• Both bind to target receptors, but T3 is ten times more active than T4

• Peripheral tissues convert T4 to T3

Figure 16.7

Hypothalamus

Anterior pituitary

Thyroid gland

Thyroidhormones

TSH

TRH

Target cellsStimulates

Inhibits

• Negative feedback regulation of TH release

• Rising TH levels provide negative feedback inhibition on release of TSH

• Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback during pregnancy or exposure to cold

Regulation of TH

Homeostatic Imbalances of TH

Figure 16.10

• Hyposecretion in adults—myxedema; endemic goiter if due to lack of iodine

• Hyposecretion in infants—cretinism

• Hypersecretion—Graves’ disease

• Autoimmune disease: body produces antibodies that activate TH-secreting cells by mimicking TSH

• Exophthalmos

Parathyroid Glands

• Four to eight tiny glands embedded in the posterior aspect of the thyroid

• Contain oxyphil cells (function unknown) and chief cells that secrete parathyroid hormone (PTH) or parathormone

• PTH—most important hormone in Ca2+ homeostasis

Figure 16.11

(b)

Capillary

Chiefcells(secreteparathyroidhormone)Oxyphilcells

Pharynx(posterioraspect)

Thyroidgland

Parathyroidglands

Trachea

Esophagus

(a)

Usually four (up to eight) tiny glands embedded in the posterior aspect of the thyroid

Parathyroid Glands

Osteoclast activityin bone causes Ca2+

and PO43- release

into blood

Hypocalcemia(low blood Ca2+)

PTH release fromparathyroid gland

Ca2+ reabsorptionin kidney tubule

Activation ofvitamin D by kidney

Ca2+ absorptionfrom food in small

intestine

Ca2+ in blood

Initial stimulus

Physiological response

Result

PTH is most important hormone for calcium homeostasis

Increases blood calcium levels 3 ways

Homeostatic Imbalances of PTH

• Hyperparathyroidism due to tumor

• Bones soften and deform

• Elevated Ca2+ depresses the nervous system and contributes to formation of kidney stones

• Hypoparathyroidism following gland trauma or removal

• Results in tetany, respiratory paralysis, and death if untreated

• Cortex

Kidney

• Medulla

Adrenal gland

Capsule

Zonaglomerulosa

Zonafasciculata

Zonareticularis

Adrenalmedulla

(a) Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla

Med

ulla

Cort

ex

• Paired, pyramid-shaped organs atop the kidneys

• Structurally and functionally, they are two glands in one

• Adrenal medulla—nervous tissue; part of the sympathetic nervous system

• Adrenal cortex—three layers of glandular tissue that synthesize and secrete corticosteroids

Adrenal (Suprarenal) Glands

Figure 16.13a

• Cortex

Kidney

• Medulla

Adrenal gland

Capsule

Zonaglomerulosa

Zonafasciculata

Zonareticularis

Adrenalmedulla

(a) Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla

Med

ulla

Cort

ex

Adrenal Cortex

mineralocorticoids

glucocorticoids

sex hormones, or glucocorticoids

Mineralocorticoids

• Regulate electrolytes (primarily Na+ and K+) in ECF

• Importance of Na+: affects ECF volume, blood volume, blood pressure, levels of other ions

• Importance of K+: sets RMP of cells

• Aldosterone is the most potent mineralocorticoid

• Stimulates Na+ reabsorption and water retention by the kidneys; elimination of K+

Mechanisms of Aldosterone Secretion

1. Renin-angiotensin mechanism: decreased blood pressure stimulates kidneys to release renin, triggers formation of angiotensin II, a potent stimulator of aldosterone release

2. Plasma concentration of K+: Increased K+ directly influences the zona glomerulosa cells to release aldosterone

3. ACTH: causes small increases of aldosterone during stress

4. Atrial natriuretic peptide (ANP): inhibits renin and aldosterone secretion, to decrease blood pressure

Figure 16.14

Primary regulators Other factors

Blood volumeand/or blood

pressure

Angiotensin II

Blood pressureand/or blood

volume

K+ in blood

DirectstimulatingeffectRenin

Initiatescascadethatproduces

Kidney

Hypo-thalamus

Heart

CRH

Anteriorpituitary

Zona glomerulosaof adrenal cortex

Enhancedsecretionof aldosterone

Targetskidney tubules

Absorption of Na+ andwater; increased K+ excretion

Blood volumeand/or blood pressure

Inhibitoryeffect

Stress

ACTH Atrial natriureticpeptide (ANP)

The RAAS Song

• Aldosteronism—hypersecretion due to adrenal tumors

• Hypertension and edema due to excessive Na+

• Excretion of K+ leading to abnormal function of neurons and muscle

Glucocorticoids (Cortisol)

• Cortisol (hydrocortisone) is the only significant glucocorticoid in humans

• Released in response to ACTH, patterns of eating and activity, and stress

• Prime metabolic effect is gluconeogenesis—formation of glucose from fats and proteins

• Promotes rises in blood glucose, fatty acids, and amino acids – saves glucose for brain

• Keep blood sugar levels relatively constant

• Maintain blood pressure by increasing the action of vasoconstrictors

Homeostatic Imbalances of Glucocorticoids

• Hypersecretion—Cushing’s syndrome

• Depresses cartilage and bone formation

• Inhibits inflammation

• Depresses the immune system

• Promotes changes in cardiovascular, neural, and gastrointestinal function

• Hyposecretion—Addison’s disease

• Also involves deficits in mineralocorticoids

• Decrease in glucose and Na+ levels

• Weight loss, severe dehydration, and hypotension

Figure 16.15

Gonadocorticoids (Sex Hormones)

• Most are androgens (male sex hormones) that are converted to testosterone in tissue cells or estrogens in females

• May contribute to

• The onset of puberty

• The appearance of secondary sex characteristics

• Sex drive

• Estrogens in postmenopausal women

Adrenal Medulla

• Chromaffin cells secrete epinephrine (80%) and norepinephrine (20%)

• These hormones cause

• Blood vessels to constrict

• Increased HR

• Blood glucose levels to rise

• Blood to be diverted to the brain, heart, and skeletal muscle

• Epinephrine stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and the heart

• Norepinephrine influences peripheral vasoconstriction and blood pressure

Adrenal Medulla

• Hypersecretion

• Hyperglycemia, increased metabolic rate, rapid heartbeat and palpitations, hypertension, intense nervousness, sweating

• Hyposecretion

• Not problematic

• Adrenal catecholamines not essential to life

Figure 16.16

Short-term stress More prolonged stress

Stress

Hypothalamus

CRH (corticotropin-releasing hormone)

Corticotroph cellsof anterior pituitary

To target in blood

Adrenal cortex(secretes steroidhormones)

GlucocorticoidsMineralocorticoids

ACTH

Catecholamines(epinephrine andnorepinephrine)

Short-term stress response

1. Increased heart rate2. Increased blood pressure3. Liver converts glycogen to glucose and releases glucose to blood4. Dilation of bronchioles5. Changes in blood flow patterns leading to decreased digestive system activity and reduced urine output6. Increased metabolic rate

Long-term stress response

1. Retention of sodium and water by kidneys2. Increased blood volume and blood pressure

1. Proteins and fats converted to glucose or broken down for energy2. Increased blood glucose3. Suppression of immune system

Adrenal medulla(secretes amino acid-based hormones)

Preganglionicsympatheticfibers

Spinal cord

Nerve impulses

Pineal Gland

• Small gland hanging from the roof of the third ventricle

• Pinealocytes secrete melatonin, derived from serotonin

• Melatonin may affect

• Timing of sexual maturation and puberty

• Day/night cycles

• Physiological processes that show rhythmic variations (body temperature, sleep, appetite)

Pancreas

• Triangular gland behind the stomach

• Has both exocrine and endocrine cells

• Acinar cells (exocrine) produce an enzyme-rich juice for digestion

• Pancreatic islets (islets of Langerhans) contain endocrine cells

• Alpha () cells produce glucagon (a hyperglycemic hormone)

• Beta () cells produce insulin (a hypoglycemic hormone)

Pancreatic islet

• (Glucagon- producing) cells

• (Insulin- producing) cells

Pancreatic acinarcells (exocrine)

Glucagon and Insulin

• Effects of Glucagon

• Major target is the liver, where it promotes

• Glycogenolysis—breakdown of glycogen to glucose

• Gluconeogenesis—synthesis of glucose from lactic acid and noncarbohydrates

• Release of glucose to the blood

• Effects of insulin

• Lowers blood glucose levels

• Enhances membrane transport of glucose into fat and muscle cells

• Inhibits glycogenolysis and gluconeogenesis

• Participates in neuronal development and learning and memory

Insulin Action on Cells

• Activates a tyrosine kinase enzyme receptor

• Cascade leads to increased glucose uptake and enzymatic activities that

• Catalyze the oxidation of glucose for ATP production

• Polymerize glucose to form glycogen

• Convert glucose to fat (particularly in adipose tissue)

Figure 16.18

Liver

Liver

Tissue cells

Stimulates glucose uptake by cells

StimulatesglycogenformationPancreas

Pancreas

Insulin

Bloodglucosefalls tonormalrange.

Stimulatesglycogenbreakdown

Bloodglucoserises tonormalrange.

Glucagon

Stimulus Bloodglucose level

Stimulus Bloodglucose level

GlycogenGlucose

GlycogenGlucose

Factors That Influence Insulin Release

• Elevated blood glucose levels – primary stimulus

• Rising blood levels of amino acids and fatty acids

• Release of acetylcholine by parasympathetic nerve fibers

• Hormones glucagon, epinephrine, growth hormone, thyroxine, glucocorticoids

• Somatostatin; sympathetic nervous system

Homeostatic Imbalances of Insulin• Diabetes mellitus (DM)

• Due to hyposecretion or hypoactivity of insulin

• Three cardinal signs of DM

• Polyuria—huge urine output

• Polydipsia—excessive thirst

• Polyphagia—excessive hunger and food consumption

• Fats used for cellular fuel lipidemia; if severe ketones (ketone bodies) from fatty acid metabolism ketonuria and ketoacidosis

• Untreated ketoacidosis hyperpnea; disrupted heart activity and O2 transport; depression of nervous system coma and death possible

• Hyperinsulinism:

• Excessive insulin secretion; results in hypoglycemia, disorientation, unconsciousness

Table 16.4

Ovaries and Placenta

• Gonads produce steroid sex hormones

• Ovaries produce estrogens and progesterone

• Estrogen responsible for:

• Maturation of female reproductive organs

• Appearance of female secondary sexual characteristics

• With progesterone causes breast development and cyclic changes in the uterine mucosa

• The placenta secretes estrogens, progesterone, and human chorionic gonadotropin (hCG)

Testes

• Testes produce testosterone that

• Initiates maturation of male reproductive organs

• Causes appearance of male secondary sexual characteristics and sex drive

• Is necessary for normal sperm production

• Maintains reproductive organs in their functional state

Other Hormone-Producing Structures

• Heart

• Atrial natriuretic peptide (ANP) reduces blood pressure, blood volume, and blood Na+ concentration

• Gastrointestinal tract enteroendocrine cells

• Gastrin stimulates release of HCl

• Secretin stimulates liver and pancreas

• Cholecystokinin stimulates pancreas, gallbladder, and hepatopancreatic sphincter

Other Hormone-Producing Structures• Kidneys

• Erythropoietin signals production of red blood cells

• Renin (an enzyme) initiates the renin-angiotensin mechanism

• Skin

• Cholecalciferol, the precursor

of vitamin D

• Adipose tissue

• Leptin is involved in appetite control, and stimulates increased energy expenditure

• Adiponectin – enhances sensitivity to insulin

Other Hormone-Producing Structures• Skeleton (osteoblasts)

• Osteocalcin prods pancreatic beta cells to divide and secrete more insulin, improving glucose handling and reducing body fat

• Thymus

• Thymulin, thymopoietins, and thymosins are involved in normal the development of the T lymphocytes in the immune response