The Endocrine System EFE Veterinary Science Anatomy and Physiology

Endocrine Glands Ductless: deliver peptides (hormones) into blood, lymph or tissue fluid Produce hormones at a site distant from effected organ/tissue Regulate most of body functions

Peptide-Target Systems The various ways in which peptides reach their targets. A, Neuroendocrine; B, endocrine; C, neurotransmitter, neuromodulator (action on postsynaptic membrane); D, paracrine (localized hormone action). 1, Bloodstream; 2, target cell; 3, synapse.

Hypophysis/Pituitary/Master Gland Compare & Save Median sections of the hypophysis of the horse (A), ox (B), pig (C), and dog (D). The rostral extremity of the gland is to the left. 1, Adenohypophysis; 2, intermediate part; 3, neurohypophysis; 4, hypophysial stalk; 5, recess of third ventricle.

Posterior Lobe (Neurohypophysis) Part of the hypothalamus (brain = neuro-) Stores and releases – Oxytocin (contraction of smooth muscle of uterus and udder myoepithelial cells) – Vasopression (Vasoconstriction, promotes fluid reabsorption by the kidneys) – These are produced by the hypothalamus Very vascular

Anterior Lobe (Adenohypophysis) Grows up from the developing dorsal mouth Products regulated by the hypothalamus – Follicle Stimulating Hormone (FSH) – Luteinizing Hormone (LH) – Adrenocorticotropic Hormone (ACTH) – Thyroid Stimulating Hormone (TSH) – Alpha-Melanocyte Stimulating Hormone (MSH) – Prolactin

Pars Intermedia (Intermediate Lobe) Lies between anterior and posterior lobes Doesn’t really do much

Brain-Pituitary-Organ Axis Organization of the brain–pituitary–peripheral organ axis. TRH, thyrotropin-releasing hormone; CRH, corticotropin-releasing hormone; DA, dopamine; PIF, prolactin-inhibiting factor; GnRH, gonadotropin-releasing hormone; SS, somatostatin; GRH, growth hormone- releasing hormone; ACTH, adrenocorticotropic hormone; TSH, thyroid-stimulating hormone; GH, growth hormone; LH, luteinizing hormone; FSH, follicle-stimulating hormone; PRL, prolactin. 1, Adrenal cortex; 2, thyroid; 3, liver; 4, ovary; 5, testis; 6, mammary gland; 7, median eminence; 8, anterior lobe of pituitary; 9, intermediate lobe of pituitary; 10, neural lobe of pituitary.

Pineal Gland Caudal Dorsal brain (in mammals) Secretes melatonin – Circadian rhythms – Taken supplementally for sleep and jet lag More dorsal and external in reptiles

Thyroid Gland Compare & Save The thyroid gland of the dog (A), horse (B), cattle (C), and pig (D). The inset to D illustrates the subtracheal connection in transverse section in the pig. 1, Isthmus; 2, trachea; 3, cricopharyngeus.

Thyroid Gland Located adherent to ventral trachea Respond to Thyroid Stimulating Hormone (TSH) produced by anterior lobe of pituitary Releases Thyroid hormone (thyroxine) – Regulates metabolism and growth Small release of Calcitonin (antagonist to parathormone)

Thyroid Gland Utilizes iodine to make thyroid hormone – Iodine deficiency causes goiter Dogs are prone to hypothyroidism Cats are prone to hyperthyroidism Compare & Save

Parathyroid Located near, attached to or embedded in the thyroid glands Set of 4 (typically) Regulate Calcium metabolism – Absorbtion from the gut – Mobilization from the skeleton – Excretion in the urine Governed by plasma calcium concentration

Adrenal Glands Compare & Save The topography of the canine adrenal glands. 1, 1′, Right and left adrenal glands; 2, left kidney; 3, aorta; 4, caudal vena cava; 5, phrenicoabdominal vessels; 6, renal vessels; 7, ovarian vein; 8, ureter; 9, bladder.

Adrenal Gland Craniomedial to kidneys – Left wraps around aorta – Right wraps around vena cava Cortex and Medulla Cortex produces mineralocorticoids, glucocorticoids and some sex steroids Medulla produces epinephrine and noreprinephrine (“fight or flight”)

Pancreatic Islet Cells Located diffusely throughout the pancreas Produce insulin and glucagon Insulin drives glucose and potassium into cells Glucagon also affects carbohydrate metabolism Also produce somatostatin, pancreatic polypeptides, and gastrin

Testicles Compare & Save Compare & Save Testis (horse). 1, Head of epididymis; 2, body of epididymis; 3, pampiniform plexus. Testis (dog) (140×). 1, seminiferous tubules (showing spermatogenesis); 2, interstitial tissue with androgen-producing (Leydig) cells.

Testicles Affected by LH and FSH Interstitial (Leydig) cells make androgens – Male sexual functioning – Accessory sex glands – Secondary characteristics – behavior Sustenacular (Sertoli) cells make inhibin and activin, which affects FSH synthesis and release

Ovaries Compare & Save Specific and functional variations in ovarian morphology. A, Ovary of a cow (monotocous). 1, Mature follicle. Specific and functional variations in ovarian morphology. B, Ovary of a bitch in a quiet stage.

Ovaries Located in dorsal abdomen Outer layer contains follicles – Each follicle contains one egg – Follicle development produces estrogen – Follicle ruptures and releases egg “scar” where follicle was becomes corpus luteum Corpora lutea produce progesterone

Placenta Present only during pregnancy Significant species variation Source of – Lactogen (mammary development) – Relaxin (prepare pelvis for parturition, helps oxytocin with expulsion of fetal membranes) Prosteglandin produced by empty uterus; (stimulated by oxytocin) promotes regression of CL and initiating next cycle – In pregnancy, fetus produces factor blocking receptivity to oxytocin, CL remains and pregnancy persisis