endocrine system. introduction the nervous system and the endocrine system coordinate functions of...

Endocrine SystemEndocrine System

IntroductionIntroduction

• The nervous system and the endocrine system coordinate functions of all body systems


• Nervous system controls body actions via nerve impulses


• Endocrine system controls body activities by releasing hormones


Two kinds of glands

1. Exocrine

2. Endocrine


• Exocrine – secrete their products into ducts

Example: salivary and sweat glands


• Endocrine – secrete hormones into blood


Endocrine glands;

1. Pituitary

2. Thyroid

3. Parathyroid

4. Adrenal

5. Pineal


• The pancreas has exocrine and endocrine functions


Stomach, intestines, and kidneys also produce hormones

Hormone ReceptorsHormone Receptors

• Although travel in blood throughout the body, they affect only specific cells


• Hormones bind to receptors on target cells


• Down Regulation – When a hormone is present in excess, a decrease in the number of receptors may occur


• Up Regulation – When a hormone is deficient, an increase in the number of receptors may occur

HormonesHormones

• Two main types;

1. Circulating

2. Local

Circulating HormonesCirculating Hormones

• Hormones that travel in blood and act on distant target cells

Local HormonesLocal Hormones

• Hormones that act locally without first entering the blood stream


Two types;

1. Paracrine

2. Autocrine


• Paracrine – act on neighboring cells


• Autocrine – act on the same cell that secreted them

Hormone ChemistryHormone Chemistry

• Some are lipid soluble and others are water soluble

Lipid-soluble hormonesLipid-soluble hormones

Include;

Steroids, thyroid hormones, and nitric oxide

Water-soluble hormonesWater-soluble hormones

Include;

Peptides, proteins, and glycoproteins

Hormone TransportHormone Transport

• Water-soluble hormones travel free in plasma

Hormone TransportHormone Transport

• Lipid soluble hormones bind to transport proteins to be carried in blood

Action of Lipid Soluble HormonesAction of Lipid Soluble Hormones

1. Hormone binds to and activates receptors within cells


2. The activated receptors alter gene expression, which results in the formation of new proteins


3. The new proteins alter the cells activity

Action of Water Soluble HormonesAction of Water Soluble Hormones

1. The hormone binds to the membrane receptor


2. The activated receptor activates a membrane G-protein which turns on adenylate cyclase


3. Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases.


4. Protein kinases phophorylate enzymes, which either become more or less active than the nonphosphorylated form

Hormonal interactionsHormonal interactions

• The responsiveness of a target cell to a hormone depends on;

1. Hormone’s concentration

2. Number of receptors

3. Influences exerted by other hormones

Hormonal interactionsHormonal interactions

• Three types;

1. Permissive

2. Synergistic

3. Antagonist

Hormonal InteractionsHormonal Interactions

1. Permissive – one hormone required to act before another can be effective


2. Synergistic – Two hormone produce an effect that is greater than the sum of individual effects


3. Antagonistic – When hormones oppose each other

Control of Hormone SecretionsControl of Hormone Secretions

• Controlled by;

1. Nervous system

2. Chemical changes in blood

3. Other hormones

4. Negative feedback

5. Positive feed back


• Negative feedback – High levels of one substance may feed back and lower the secretion of the other substance


• Positive feedback – high levels of one substance may feedback and increase the secretion of the other substance

Pituitary GlandPituitary Gland

• Hypophysis


• Located in the sella turcica of the sphenoid bone


1. Anterior pituitary (adenohypophysis)

2. Posterior pituitary (neurohypohysis)

Anterior PituitaryAnterior Pituitary

• Hormones of the A.P. are controlled by hormones produced by the hypothalamus


• Hormones1. Human growth hormone (hGH)2. Thyroid-stimulating hormone (TSH)3. Follicle-stimulating hormone (FSH)4. Luteinizing hormone (LH)5. Prolactin (PRL)6. Adrenocorticotropic hormone (ACTH)7. Melanocyte-stimulating hormone (MSH)


• Hormones travel from the hypothalamus to the A.P. via a vascular network called the hypophyseal-portal system


hGH – essential for normal body growth responsible for growth spurt during

puberty inhibits cell glucose uptake


• Controlled by Growth hormone-releasing hormone (GHRH)

DwarfismDwarfism

• Deficiency in hGH

GigantismGigantism

• Excess hGH in kids

AcromegalyAcromegaly

• Excess hGH in adults


TSH causes thyroid to secrete thyroid

hormone


TSH Controlled by TRH (thyrotropin releasing

hormone)


TSH High levels of thryoid hormone feed back

and inhibit TSH secretion


TSH Low levels of thyroid hormone cause

TSH levels to go up


FSH In females, FSH initiates follicle

development and secretion of estrogens in the ovaries


FSH In males, FSH stimulates sperm

production in the testes


• FSH – Controlled by Gonadotropic-releasing hormone (GnRH)


LH In females, LH stimulates secretion of

estrogen by ovarian cells to result in ovulation


LH In males, LH stimulates the interstitial

cells of the testes to secrete testosterone


• LH – controlled by GnRH


PRL High levels of progesterone, estrogen

and prolactin during pregnancy promotes breast growth


PRL Estrogen blocks the milk-secreting action

of PRL


PRL During labor, the estrogen-secreting

placenta is delivered. After that, PRL causes the breasts to secrete milk.


PRL Suckling promotes PRL secretion


• Controlled by Prolactin–releasing hormone (PRH)


ACTH controls the production and secretion of

glucocorticoids (cortisol) by the cortex of the adrenal medulla


ACTH Stress stimulates ACTH release, which in

turn stimulates cortisol release.


• Controlled by Corticotropin-releasing hormone (CRH)


MSH increases skin pigmentation


• Controlled by CRH

Posterior PituitaryPosterior Pituitary

Does not synthesize hormones


It does store and release oxytocin (OT) and antidiuretic hormone (ADH)


These hormones are made by the hypothalamus and stored in the P.P.


The neural connection between the hypothalamus and the P.P. is via the hypothalmohypophyseal tract


OT stimulates contraction of the uterus

during labor


OT Stimulates ejection of milk from the

breasts


OT As uterine contractions and cervical

dilation increase during labor, they have positive feedback on the P.P. and increases OT secretion.


OT stimulated by suckling


ADH Stimulates water reabsorption by the

kidneys


ADH effect of ADH is to decrease urine

volume and conserve body water


ADH controlled by osmotic pressure of the

blood, which is monitored by the hypothalamus


ADH Dehydration stimulates ADH secretion


ADH Alchohol inhibits ADH secretion,

increasing the urine output

Diabetes InsipidusDiabetes Insipidus

Due to lack of ADH secretion or when the kidneys are resistant to ADH

ThyroidThyroid

Located below the larynx and has r. and l. lateral lobes

ThyroidThyroid

consists of thryoid follicles

ThyroidThyroid

Follicular cells secrete thyroxine (T4) and triiodothyronine (T3)

ThyroidThyroid

Parafollicular cells secrete calcitonin (CT)

Thyroid HormonesThyroid Hormones

Increases metabolism


Crucial for brain development


• Up regulates beta receptors in the heart


Important for growth and skeletal maturation


Crucial for G.I. motility

ThyroidThyroid

If you produce excess thyroid hormone, it feeds back and inhibits TSH secretion

ThyroidThyroid

If the thyroid hormone levels decline, there is less negative feedback on the pituitary

CalcitoninCalcitonin

• Reduces blood calcium levels

ParathyroidParathyroid

Parathyroid Glands are embedded on the posterior surfaces of the lateral lobes of the thyroid


Produces parathyroid hormone (PTH)


PTH increases blood calcium levels and decreases blood phosphate levels


PTH secretion controlled by blood calcium and phosphate levels directly via negative feedback loops

Adrenal GlandsAdrenal Glands

Located superior to the kidneys

Adrenal GlandsAdrenal Glands

Consists of an outer cortex and an inner medulla

Adrenal CortexAdrenal Cortex

Divided into three zones


1. Zona glomerulosa (outer zone) – secretes mineralcorticoids (aldosterone)


Aldosterone decreases potassium levels and increases sodium levels


Aldosterone is stimulated by Angiotensin II


2. Zona fasciculata (middle zone) – secretes glucocorticoids (cortisol)


Cortisol increases blood glucose levels by suppressing insulin and via gluconeogenesis


Cortisol is an immunosuppressant


Cortisol raises blood pressure


Cortisol controlled by CRH and ACTH


3. Zona reticularis (inner zone) – secretes androgens (testosterone)

Adrenal MedullaAdrenal Medulla

Secretes epinephrine and norepinephrine

PancreasPancreas

• Endocrine and exocrine gland

PancreasPancreas

• Located posterior and slightly inferior to the stomach

PancreasPancreas

• Its exocrine secretions are drained by the pancreatic duct into the duodenum

PancreasPancreas

• Contains over a million islets of langerhans

PancreasPancreas

• It mainly consists of clusters of cells (acini)

• These are enzyme-producing exocrine cells

PancreasPancreas

• Four types of cells in the Pancreatic Islets

PancreasPancreas

1. Alpha cells secrete glucagon which increases blood glucose levels

PancreasPancreas

• Beta cells secrete insulin which decreases blood glucose levels

PancreasPancreas

• Delta cells secrete somatostatin, which acts as a paracrine and inhibits the secretion of insulin and glucagon

PancreasPancreas

• F-cells secretes pancreatic polypeptide, which regulates release of pancreatic digestive enzymes

PancreasPancreas

• Glucagon and insulin are controlled by negative feedback

Pancreas/Negative FeedbackPancreas/Negative Feedback

• Glucagon is released during fasting or hypoglycemia

Pancreas/Negative FeedbackPancreas/Negative Feedback

• Glucagon promotes glycogenolysis and gluconeogenesis

PancreasPancreas

• Insulin is secreted after meals

PancreasPancreas

• Insulin increases glucose uptake by muscle and fat cells

PancreasPancreas

• Insulin stimulates glycogenesis

PancreasPancreas

• Insulin stimulates lipogenesis

PancreasPancreas

• Insulin increases amino acid uptake into cells and increases protein synthesis

PancreasPancreas

• Insulin inhibits lipolysis

Diabetes MellitusDiabetes Mellitus

• Type I – It is caused by an autoimmune destruction of beta cells

Diabetes MellitusDiabetes Mellitus

• Type II – Due to obesity. As obesity progresses, they develop insulin resistance

OvariesOvaries

• Lie in pelvic cavity and produce sex hormones (estrogens and progesterone)

OvariesOvaries

These hormones responsible for;

1. Development and maintenance of female sexual characterisics

OvariesOvaries

2. Reproductive cycle

OvariesOvaries

3. Pregnancy

OvariesOvaries

4. Lactation

TestesTestes

Lie inside the scrotum and produce testosterone

TestesTestes

• Testosterone related to the development and maintenance of male sexual characteristics

Pineal GlandPineal Gland

• Attached to the roof of the third ventricle

Pineal GlandPineal Gland

• Secretes melatonin

Seasonal Affective DisorderSeasonal Affective Disorder

• SAD

• Due to over-production of melatonin

ThymusThymus

• Secretes several hormones related to immunity

ThymusThymus

• Thymosin (hormone) – promote maturation of T cells (white blood cell involved in immunity)

endocrine system. introduction the nervous system and the endocrine system coordinate functions of...

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