GENERAL FUNCTION OF ENDOCRINE

SYSTEM

PHYSIOLOGY DEPARTEMENTMEDICAL SCHOOL OF

UNIVERSITAS SUMATERA UTARA

Location of Major Endrocrine OrgansLocation of Major Endrocrine Organs

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 9.3

HYPOTHALAMUS• The release of hormones from both the posterior

and anterior pituitary is directly controlled by hypothalamus

• Posterior pituitary connects to hypothalamus by a neural pathway

• Anterior pituitary connects to the hypothalamus by unique vascular link

Hypothalamic hormones

Thyrotropin RH (TRH) Thyrotropin, Prolactin

Gonadotropin RH (GnRH) LH, FSH

Corticotropin RH (CRH) Adrenocorticotropin

Hormone Target Pituitary Hormone

Growth hormone RH (GHRH) Growth hormone

Prolactin-inhibiting factor (PIF) Prolactin, Thyrotropin(Dopamine)

Growth hormone IH (GHIH) Growth hormone(somatostatin)

Complex endocrine pathways involvingpituitary and hypothalamus

Hormones of the Pituitary Gland

Hormones of the Pituitary Gland

• Neurohormones

• Synthesized by neurons in the supraoptic and paraventricular nuclei

• Small peptides synthesized in the cell bodies and transported to the posterior pituitary by specific carrier proteins

Antidiuretic hormone (ADH) and oxytocin

Antidiuretic Hormone (ADH)

• Antidiuretic actions

• Vasopressor actions

- increases permeability of the collecting ducts to water

- V2 receptors

- constricts vascular smooth muscle cells- V1 receptors, non-hormonal

diabetes insipidus

Oxytocin• Breast-feeding

• Childbirth (parturition)

- contracts the myoepithelial cells of the alveoli

- classic neuroendocrine reflex

- in late pregnancy, uterine smooth muscle (myometrium) becomes sensitive to oxytocin

- positive feedback

Breast-feeding

Parturition

Growth Hormone

• Does not have a target gland as other

pituitary hormones.

• Promotes growth in all tissues.

• Major targets: protein and lipid metabolism

• Mechanisms: transcriptional and translational

Physiologic effects of GH

• Anabolic effects:– promotion of protein synthesis and amino acid

transport – decreased catabolism of proteins and amino

acids• Stimulation of bone growth and cartilage

formation:– Cell division and protein synthesis– Differentiation of condrocites to osteogenic

cells and deposition of bone

PROLACTIN• Breast is main site of action.• Episodic release• PRL secretion induced by high estrogen and hCG• PRH → oxytocin PRL inhibitor : PIH (dopamine)

most dominant

• PRL inhibits LHRH secretion• TRH can act as a PRL stimulator

Secretion: mediated through hypothalamus-pituitary secretions

Steroidal hormones: Thyroxine (T4) and Triiodothyronine (T3):

both regulate production of ATP from glucose, affects metabolic rate

Calcitonin: lowers blood calcium levels

Thyroid Gland

PHYSIOLOGICAL EFFECTS OF THYROID HORMONES

• Increase O2 consumption of almost all active tissues

(in part by mobilising fatty acids)• Increase cardiac output • Needed for normal brain development• Needed for normal growth and skeletal

maturation

Negative feedback homeostasis:

T3 and T4 effects on TSH and TRH

Secretion: response to lowered blood calcium levels

Hormone: Parathyroid hormone (PTH), nonsteroidal

Removes calcium and phosphate from bone

Increases absorption of calcium by the digestive tract

Increases renal retention of calcium and excretion of phosphate

Parathyroid Glands

Structures: islets of Langerhans

Hormones: nonsteroidal Glucagon: made by alpha cells, raises

blood sugar Insulin: made by beta cells, lowers blood

sugar

Pancreas: Endocrine Functions

Roles of Insulin and Glucagon in Regulating Blood Glucose

Adrenal Gland

epinephrinenorepinephrine

cortisolaldosterone

Cortisol exerts negative feedback on ACTH and CRH

Cortisol effectsSynergizes glucagonand epinephrine

Secretion of Cortisol

Cortisol Effects

Increases in blood[glucose] (gluconeogenesis and glycogenolysis)[amino acids] (protein catabolism)[fatty acids] (lipolysis)

Permissive for action of glucagon and epinephrine(synergism)

Anti-inflammatory (prevents actions of cytokines)

Negative feedbackreduces CRH (hypothalamus)reduces ACTH (anterior pituitary)

Adrenal medulla: neuroendocrine organ Secretion: sympathetic nervous system Hormones: nonsteroidal

Epinephrine and Norepinephrine: enhance function of sympathetic nervous system (Fight or flight)

Adrenal Glands: Medulla

Roles of the Hypothalamus and Adrenal Glands in the Roles of the Hypothalamus and Adrenal Glands in the Stress ResponseStress Response

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

LH and FSH

LH / FSH functionO vary

ovaoes trog en

p rog es teron e

Tes tessp erm

tes tos te ron e

TESTES

• Testosterone synthesised from Leydig cells

• LH stimulates this release• Sertoli cells play important role in

spermatogenesis• FSH stimulates Sertoli cells

OVARIES

• FSH stimulate follicle maturation

• Granular cell secrete estrogen

• LH stimulate follicle maturation in the last periode and surge preceeds ovulation

• Corpus luteum secrete progesteron

• Mechanism negative feed back from progesteron and estrogen reduce FSH/LH

Hormone: testosterone (steroidal)

Functions:

Regulates development and normal

functioning of sperm, male reproductive

organs, male sex drive

Development of male secondary sex

characteristics

Testes

Hormones (steroidal) and functions:

Estrogen: initiates development of

secondary sex characteristics, regulates

menstrual cycle

Progesterone: regulates menstrual cycle

Ovaries