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
parathormone)
Thyroid Gland
• Utilizes iodine to make thyroid hormone
– Iodine deficiency causes goiter
• Dogs are prone to hypothyroidism
• Cats are prone to hyperthyroidism
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
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
Testis (dog) (140×). 1,
seminiferous tubules
(showing
spermatogenesis); 2,
interstitial tissue with
androgen-producing
(Leydig) cells.
Testis (horse). 1, Head of epididymis;
2, body of epididymis; 3,
pampiniform plexus.
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
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