The Endocrine System

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
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 hormonereleasing 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
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
Thyroid Gland
• Utilizes iodine to make thyroid hormone
– Iodine deficiency causes goiter
• Dogs are prone to hypothyroidism
• Cats are prone to hyperthyroidism
• 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
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,
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
• Also produce somatostatin, pancreatic
polypeptides, and gastrin
Testis (dog) (140×). 1,
seminiferous tubules
spermatogenesis); 2,
interstitial tissue with
(Leydig) cells.
Testis (horse). 1, Head of epididymis;
2, body of epididymis; 3,
pampiniform plexus.
• 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
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.
• 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
• 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