Download Dissection of the Brain, Hypothalamus and Pituitary

ANS 3319C Reproductive Physiology and Endocrinology Lab
Hypothalamic and Pituitary Anatomy & Endocrinology
Objectives
1) To provide an introduction to the gross anatomy of the brain with emphasis on dissection of the
hypothalamus and pituitary.
2) To introduce the anatomical, neural, and vascular relationships between the hypothalamus and
the pituitary (anterior and posterior), which allow them to communicate with each other.
3) To provide an introduction to hormones synthesized/secreted by the hypothalamus and the
anterior and posterior pituitary with emphasis on reproductive hormones.
Gross Anatomy of the Brain (Figure 5)
Cerebrum: center of higher mental functions, voluntary muscle control.
Cerebellum: controls the property of movements, speed, acceleration, and trajectory.
Brainstem: midbrain: auditory and visual reflex centers.
pons, medulla: postural reflexes and other reflex centers.
Olfactory bulb: involved in distinguishing smell.
Optic chiasma: where the optic nerves cross to contralateral sides.
Pituitary: composed of neurohypophysis and adenohypophysis; master gland controlling body’s
internal environment.
Corpus collosum: the commissure between the hemispheres of the brain.
Pineal body: synthesis and secretion of melatonin.
Hypothalamus: controls body’s internal environment.
Stalk median eminence: area between the hypothlalmus and the pituitary.
Mammillary body
Third ventricle of the brain
Anatomy of the Hypothalamus, Pituitary & Pineal Gland
Hypothalamus (Figures 1 & 5)
•
Neuroendocrine gland comprised of numerous paired nuclei that integrate physiological
signals of the body.
•
Occupies a small portion of the third ventricle, extending from the optic chiasma to the
mammillary bodies.
•
Synthesizes and secretes hormones that act on the pituitary (See Hormone Table):
Releasing & Inhibiting hormones: small peptides secreted from hypothalamus that
control the secretion of protein hormones from the pituitary gland
Hormones directly associated with reproduction: GnRH, CRH, PIF, PRF
Two important nuclei related to reproduction, which secrete GnRH:
Arcuate nucleus - controls basal secretion of LH and FSH.
Preoptic nucleus - controls preovulatory surge of LH and FSH.
Hormones indirectly associated with reproduction: TRH, GHRH, GHIH
Hormones
Oxytocin - released from paraventricular nucleus (PVN).
Vasopressin - released from supra-optic nucleus (SON).
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 2
AH – adenohypophysis
AHA – anterior hypothalamic area
ARC – arcuate nucleus
DHA – dorsal hypothalamic area
DMN – dorsal medial nucleus
MB – mammillary body
ME – median eminence
NH – neurohypophysis
OC – optic chiasm
PHA – posterior hypothalamic area
PM – premammillary nucleus
PON – preoptic nuclei
PT – pars tuberalis
PVN – paraventricular nuclei
SCN – suprachiasmatic nucleus
SON – supraoptic nuclei
VMN – ventromedial nucleus
Figure 1. Schematic drawing of hypothalamic nuclei and pituitary from the side (top) and frontal view (bottom).
Median Eminence (Figures 1, 2)
•
Area where hypothalamic hormones are released from nerve endings into the capillary
plexus called the hypophyseal portal blood system that serves the anterior pituitary.
Hypophyseal Portal Blood System (Figures 2, 4)
•
Capillary system that transports hypothalamic releasing/inhibiting hormones via a
vasculature system to the anterior pituitary; allowing for “communication between the
hypothalamus and anterior pituitary.” Prevents hormones from entering the general
circulation where they would be degraded quickly.
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 3
Pituitary (Hypophysis) (Figures 1,2,3,5)
•
Sella turcica - bony depression located in sphenoid bone that houses and protects the
pituitary gland. Named because it resembles a side view of the seat of a Turkish saddle.
•
Origin of Pituitary Gland (See Figure 3)
•
Posterior pituitary (Neurohypophysis)
Arises from embryonic brain tissue. Hence, it is physically connected to hypothalamus.
Median eminence
Infundibular stem
Pars nervosa - neural lobe where oxytocin and vasopressin are stored and secreted.
•
Anterior pituitary (Adenohypophysis)
Arises from embryonic gut tissue from roof of mouth. Hence, it is not physically
connected to hypothalamus and receives hormones via hypophyseal portal blood system.
Pars intermedia - synthesizes and secretes melanocyte stimulating hormone.
Pars tuberalis - pituitary stalk.
Pars distallis - forms major portion of adenohypophysis.
Reproductive hormones: LH, FSH, ACTH, Prolactin
Other hormones: GH, TSH
Figure 2. Schematic providing an anatomical overview of the hypothalamic-pituitary axis.
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 4
Figure 3 Early embryonic development of the anterior and posterior lobes of the pituitary (Figure 4.3 Senger text).
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 5
Figure 4. Diagramatic view of the hypophyseal portal system between the hypothalamus and the pituitary and a
photograph showing the intense vascularity of the portal system (Figure 5.5; Senger text)
Pineal Gland (Figure 5)
•
Posterior to the hypothlamus and between the cerebral hemispheres of the brain.
•
Responds to changes in photoperiod sensed by visual system of mammals.
•
Melatonin - hormone produced by pineal gland.
•
Secretion is enhanced by the onset of darkness.
•
Regulates reproductive function in seasonal breeding animals (i.e., sheep, horses,
numerous wild animals) by inhibiting or stimulating gonadal function.
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 6
Figure 5. Gross anatomy of the equine brain – ventral view and sagittal section.
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 7
Summary of endocrine glands and hormones they secrete
Gland
Hormone
Class
Function
Hypothalamus
Gonadotropin Releasing Hormone (GnRH)
Prolactin Inhibiting Factor (PIF)
Prolactin Releasing Factor (PRF)
Thyrotropin Releasing Hormone (TRH)
Corticotropin Releasing Hormone (CRH)
Growth Hormone Releasing Hormone (GHRH)
Growth Hormone Inhibiting Hormone (GHIH)
(Also known as Somatostatin)
Peptide
Peptide
Peptide
Peptide
Peptide
Peptide
Peptide
Stimulates release of FSH and LH
Inhibits prolactin release
Stimulates prolactin release
Stimulates release of TSH, prolactin, GH (cattle & rats)
Stimulates release of ACTH
Stimulates release of GH
Inhibits release of GH
Oxytocin and Antidiuretic Hormone (ADH)
Peptide
Produced in HYPOTH but stored in the posterior pituitary
Growth Hormone (GH)
Protein
Promotes tissue growth and general metabolism
Adrenocorticotropic Hormone (ACTH)
Peptide
Stimulates the adrenal cortex
Thyrotropic Stimulating Hormone (TSH)
Glycoprotein
Stimulates release of thyroid hormones
Follicle Stimulating Hormone (FSH)
Glycoprotein
Stimulates follicular growth, spermatogenesis, estrogen release
Luteinizing Hormone (LH)
Glycoprotein
Ovulation - CL formation, function and progesterone secretion
Secretion of estrogen and androgens
Prolactin (PRL)
Protein
Promotes lactation and maternal behavior
Stimulates CL formation and progesterone secretion some species
Antidiuretic Hormone (ADH)
Peptide
Water conservation, smooth muscle contraction
Oxytocin
Peptide
Smooth muscle contraction, parturition, milk letdown
Luteolytic action, sperm and egg transport
Thyroid
Thyroxin (T4)
Triiodothyronine (T3)
Modified AA
Enhances protein synthesis, increases general metabolism
Pineal Gland
Melatonin
Modified AA
Regulates gonadal function in seasonal breeding animals
Anterior Pituitary
Posterior Pituitary
ANS 3319C Reproductive Physiology and Endocrinology Lab – Hypothalamic and Pituitary Anatomy & Endocrinology 8
Gland
Hormone
Class
Function
Parathyroid
Parathyroid Hormone
Peptide
Regulates calcium and phosphorous metabolism
Pancreas
Insulin
Glucagon
Protein
Peptide
Regulates carbohydrate metabolism
Regulates carbohydrate metabolism
Adrenal Medulla
Epinephrine
Norepinephrine
Modified AA
Modified AA
Augments sympathetic nervous system, prepares for emergencies
Energy mobilization, activates adenylate cyclase
Adrenal Cortex
Glucorticoids (cortisol, cortisone, corticosterone)
Steroid
Initiation of parturition, milk synthesis, energy metabolism
Decreases inflammatory and immunologic responses
Mineralocorticoids (aldosterone)
Steroid
Regulate sodium and potassium metabolism
Estrogen (from follicles)
Steroid
Promotes female sex behavior; maintenance of female duct system
Stimulates secondary sex characteristics; anabolic actions
Stimulates calcium uptake in bones
Mammary growth and development
Uterine contractions and secretions
Progesterone (from corpus luteum - CL)
Steroid
Preparation and maintenance of uterus for pregnancy
Stimulates endometrial secretions
Prepares mammary gland for lactation
Control of gonadotroptin secretion; anabolic effects
Inhibins
Protein
Prevents release of FSH
Testis
Testosterone
Steroid
Male mating behavior and stimulates secondary sex characteristics
Development and maintenance of male duct system
Spermatocytogenesis
Anabolic effects
Placenta
Equine Chorionic Gonadotropin (eCG)
Estrogens/Progesterone
Placental Lactogen
Glycoprotein
Steroid
Glycoprotein
Formation of accessory CL - progesterone synthesis
See ovary
Stimulates mammary growth and secretions; nutrient flow to fetus
Uterus
Prostaglandin F2α
Relaxin
Lipid
Protein
Regression of CL and initiation of parturition
Dilates cervix
Ovary