FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
ANATOMY
Also known as: hypophysis
It’s a small gland with a diameter of 1cm and weighs about 0.5 to 1 gram
Situated at the sella turcica
Connected to the hypothalamus via the
Pituitary stalk Pituitary Land has 2 lobes
1. Anterior Pituitary (Adenohypophysis)
Originates embriologically through the invagination of the pharyngeal epithelium or Rathke’s pouch
2. Posterior Pituitary (Neurohypohysis)
Originates from the neural tissue outgrowth from the hypothalamus Contains large glial cells
MAJOR TYPE OF CELLS IN THE ANTERIOR LOBE
1. Chromophils
o Granulated secretory cells
2 types of Chromophils a. Acidophils – 80%, majority Somatotrophs – growth hormone (50%) Lactotrophs – prolactin (10-30%) b. Basophils Gonadotrophs – FSH and LH (20%)
Corticotrophs – ACTH and MSH (10%)
Thyrotrophs – TSH (5%)
2. Chromophobes
o Degranulated secretory cells
POSTERIOR PITUITARY HORMONES
The posterior pituitary gland does not produce any hormone. It only stores the hormones that are secreted by the hypothalamus particularly in the magnocellular neurons (supraoptic and paraventricular).
2 hormones secreted by the posterior pituitary gland: 1. Anti-diuretic hormone – produced in the
supraoptic nuclei of the hypothalamus
2. Oxytocin – produced in the paraventricular
nuclei of the hypothalamus
This hormones are transported from the hypothalamus to the posterior pituitary gland via axoplasm neuron nerve fibers
The section of posterior pituitary is controlled by the nerve signals that originate from the hypothalamus and terminate in the posterior pituitary
PHYSIOLOGY B: PITUITARY GLAND
DRA. GAMBOA
FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
There are no releasing and inhibiting hormonesANJTERIOR PITUITARY HORMONES
The sections in controlled by:
o Hypothalamic Releasing Hormones Released from the
hypothalamus and goes to the target endrocrine glands
o Hypothalamic Inhibitory Hormones
Hormones Target gland Action
Thyrotropin – releasing hormone (TRH) Anterior Pituitary Stimulates secretion of trophic hormones (TSH) Gonadotrophin – releasing hormone (GnRH) Anterior Pituitary Stimulates secretion of gonadotropes (FSH, LH) Corticotropin – relaeasing hormone (CRH) Anterior Pituitary Stimulates secretion of coticotropes (ACTH) Growth hormone - releasing hormone (GHRH) Anterior Pituiatry Stimulates secretion of somatotropes (GH) Growth hormone – inhibitory hormone (somatostatin) Anterior Pituiatry Inhibits secretion of somatotropes (GH) Prolactin – Inbibiting hormone (PIH) Anterior Pituiatry Inhibits synthesis and secretion of lactotropes (prolactin) ENDOCRINE AXIS
Three levels of Endocrine Axis:
1. Hypothalamus 2. Pituitary Gland
3. Peripheral Endocrine Gland
ADRENOCORTICOTROPIC HORMONE (ACTH)
Produced by corticotropes
Stimulates the release of some adrenocortical hormone in the adrenal cortex
Affects 2 zones in the adrenal cortex: Zona Fasiculata (Cortisol) and Zona Reticularis (Androgen)
Affects metabolism of glucose, proteins and fats Has diurinal pattern with a peak in early
morning and a valley in the later afternoon Secretion of CRH and ACTH is pulsatile
Regulators:
Stress (neurogenic: fear and systemic: infection) – stimulates adrenal cortex to release cortisol Hypothalamus -> release CRH -> stimulate pituitary gland -> release ACTH -> stimulates adrenal cortex -> release cortisol
Effects:
Decrease in the blood glucose
FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
THYROID STIMULATING HORMONE (TSH)
One of the pituitary glycoprotein hormones (TSH, LH and FSH)
Thyrotropes – regulates thyroid function by secreting the hormone thyroid stimulating hormone
Release during diurinal rhythm o Highest in overnight o Lowest in dinnertime
It is a hetero dimer composed of alpha subunit, called the alpha-glycoprotein subunit and beta subunit
o Alpha subunit is common to TSH, FSH and LH
o Beta subunit is specific
Hypothalamic-Pituitary-Thyroid Axis
Hypothalamus -> release TRH -> stimulates the anterior pituitary -> release TSH -> stimulate the thyroid gland -> release thyroid hormones T3, T4
Effect
Thyrotropin control the rate of section of T3 and T4 which control the rate of most intracellular reactions in the body
If there is a release of T4, peripherally it will be converted into T3. Target tissues: Heart, liver, gonads, CNS.
If there is an increase T3 and T4 there will be a negative feedback to the pituitary gland and the hypothalamus
TSH also has a strong tropic effect and stimulates hyperthrophy, hyperplasia, and survival of thyroid epithelial cells
GONADOTROPIN RELEASING HORMONE (GnRH)
Gonadotrope secretes FSH and LH Secreted in a pulsatile manner
Secretions:
1 pulse per hour – increase in LH secretion (luteal phase)
1 pulse in 3 hours – increase in FSH secretion (follicular phase)
Continuous infusion – down regulation/decrease of receptors
Hypothalamic-Pituitary-Gonadal Axis
Hypothalamus -> release GnRH (LHRH) -> stimulates anterior pituitary -> release of LH and FSH -> stimulates gonads (ovaries and testis) -> release of estrogen, progesterone, testosterone, inhibin
The FSH will stimulates the ovaries/testis to produce Inhibin
Increase levels of Inhibin will cause a negative feedback to the hypothalamus and pituitary gland
In women, progesterone and testosterone has a negative feedback on the gonadotropic function at the level of hypothalamus and pituitary
Estrogen levels
A low dose of estrogen – negative feedback on FSH and LH secretion
High estrogen levels – maintained for 3 days cause a surge in LH (ovulation will occur) and to a lesser extent, FSH secretion (positive feedback)
PROLACTIN
Produced by Lactotrope
Structurally related to GH and HPL (Human Placental Lactogen)
Acts on non-endocrine cells: mammary gland It is normally under tonic inhibition by the
hypothalamus: Dopamine
It is one of the many hormones released in response to stress
Stimulated by TRH and PRH
Actions:
FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
milk production Increase prolactin will increase dopamine thus inhibiting GnRH. This will decrease FSH and LH and will inhibit ovulation
Inhibits spermatogenesis via decrease in GnRH
Factors that increase Prolactin Secretion o Breastfeeding
o Dopamine Antagonist o Sleep
o Strees o Estrogen
Factors that decreases the Prolactin Secretion o Dopamine
o Dopamine Agonist o Somatostatin
o Increase prolactin will cause a negative feedback
Abnomalities of Prolactin Secretion: 1. Hypoprolactinemia
- Failure to lactate
2. Hyperprolactinemia
- Galactorrhea
- Inhibition of GnRH will cause amenorrhea that will cause failure to ovulate
- A decrease in testosterone will cause a loss of potency and libido
GROWTH HOROMONE
Produced by somatotropes
Also called as somatotrophic hormone or somatotropin
Half-life: 6-20mins
Plasma lever is higher in infants and children than in adults.
Has diurinal rhythm: peak is in morning before awakening and lowest during the day
Secretion is pulsatile One of the stress hormone Also released during stress
Hypothalamus -> release GHRH -> stimulated the anterior pituitary -> release of GH -> targets: bones, tissues, muscles and the liver
Metabolic Effects of Growth hormone:
1. Anabolic
o Stimulates transport of amino acids into the cell thus increasing cell CHON which will be used information of proteins and represses proteolysis
2. Diabetogenic
o Inhibits utilization of free fatty acids o Increase insulin secretion -> beta cells
exhaustions -> insulin resistance
3. Ketogenic
o Lipolysis -> increase breakdown of stored fat -> increase free fatty acids ->ketosis
o Increase acetoacetic acid in the liver
Direct Effects of Growth Hormone:
1. Decrease glucose uptake and utilization by the cells
2. Increase lipolysis
3. Increase protein synthesis in muscle cells thus increasing the lean body mass
4. Production of IGF-1 in the liver
Insulin-like growth factor type 1 (IGF-1)
Stimulate uptake of amino acid in the target cells that promotes protein synthesis thus promoting linear growth
Increase protein synthesis in muscle cells will increase body mass
Increase protein synthesis in most organs will increase organ size
FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
realeasing now the Free Fatty AcidsGH releases Ghrelin
Ghrelin – is found in the stomach. It increased your appetite
GH secretion is increased by:
o Decrease blood glucose (hypoglycemia) – most potent stimulator
o Decrease blood free fatty acid o Starvation or fasting
o Ghrelin
o Protein Deficiency
o Trauma, stress, excitement o Exercise
o Testosterone o Estrogen
o Deep Sleep (stage II and IV) o GHRH
GH secretion is decreased by: o GHIH – Somatostatin o Increased somatomedin o Obesity
o Hyperglycemia o Aging
o Increased blood Free Fatty acid o Exogenous GH
ABNORMALITIES OF THE PITUITARY GLAND
1. Panhypopituitarism
- Affects both anterior and posterior pituitary gland
- Decrease secretion of all anterior pituitary hormones
- It can be: congenital, occurs suddenly or slowly at any time during life, results from a pituitary tumor
A panhypopituitarism in adult
- Conditions could be:
craniopharyngiomas/chromophobe tumor
- General Effects: hypothyroidism, decrease production of glucocorticoid, suppressed secretion of gonadotropic hormones
2. Frolich’s Syndrome
- Adipogenitalis syndrome (involves hypothalamus and pituitary gland)
Adiposogenital Dystrophy
- Usually associated with tumours of the hypothalamus causing increased appetite and depressed secretion of gonadotropin
- Rare childhood metabolic disorder characterized by: obesity, growth retardation and retarded development of the genital organs.
3. Simmond’s Disease
- Destruction of hypothalamus and pituitary gland
4. Sheehan’s Syndrome
- Destruction of adenohypophysis during pregnancy due to massive bleeding thus causing necrosis of the pituitary gland
ABNORMALITIES ASSOCIATED WITH GROWTH HORMONE
Dwarfism
FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
secretion Well-proportional
Does not pass through puberty No hypothyroidism
No mental retardation Could have sexual infantilism Cute dwarf
Other Dwarfism
1. Laron Dwarfism
- GH insensitivity due to a defect in GH receptors and a marked decrease in IGF-1
2. African Pygmies
- Rate of GH secretion is normal or high but IGF-1fails to increase at the time of puberty
3. Glucocorticoid excess 4. Cretinism
- Thyroid hormone deficiency - Ugly dwarf
Excess in Growth Hormone 1. Gigantism
- Excessive GH secretion before adolescence -> giant
- Full blown diabetes mellitus -> increase blood glucose level (hyperglycemia)
2. Acromegaly
- Acidophilic tumors occur after adolescence
- Bone can become thicker, soft tissues can continue to grow
- Enlargement of hands and feet - Course facial features
- Visceralomegaly (tongue, liver, kidney) - Skin thickening
ANTI-DIURETIC HORMONE (ADH)
Short polypeptide, 9 amino acid residue Uses the following receptors
o V1a – vasoconstrictive effects o V2 – antidiuretic effects Half-life = 15-20mins
Essential for water balance
kidneys (DCT nad CD)
Excitatory Stimuli for ADH Release o Increased ECF osmolality o Hypotension o Pain o Emotion, Stress o Exercise o Warm/Hot Environment o Standing o Angiotensin
o Nicotine, Clofibrate, Carbamazipine
Decrease H20 -> increase ECF osmolality -> increase secretion of ADH -> increase H20 permeability in DCT and CD -> decrease urine volume, increase urine tonicity, decrease ECF osmolality to normal
Inhibitory Factors for ADH Release o Decrease ECF osmolality o Overhydration
o Hypertension o Hypervolemia o Alcohol intake
o Cold/cool environment
Excess body H20 -> decrease osmolality -> inhibition of ADH secretion -> decrease H2O reabsorption in DCT and CD -> increase urine volume, decrease urine tonicity and ECF osmolality increases to normal
DISORDERS OF ADH SECRETION
1. Central Diabetes Insipidus
- Decrease ADH secretion
2. Nephrogenic Diabetes Insipidus
Absence of receptors for ADH in the DCT and CD
Clinical Features:
Polyuria Polydipsia Hypotension
FEU-NRMF INSTITUE OF MEDICINE: PHYSIOLOGY B
SEC 1G
Hypernatremia Increase ECF osmolality
3. Syndrome of Inappropriate Secretion of ADH
- Increase secretion of ADH
- Possibly due to tumors, bronchogenic cancers
Clinical Features
Water retention and weight gain Edema
Hypertension Serum dilution
OXYTOCIN
Increased oxytocin will stimulate estrogen that will dominates uterus to contract and initiate labor
Orgasm will stimulate oxytocin release thus contracting uterus to facilitate transport of sperm
Suckling the nipple
Actions of Oxytocin
1. Contraction of the myoepithelial cells in the mammy glands
- Milk is forced from the alveoli into the ducts and delivered to the infant - Mechanism: Milk letdown or Milk
Ejection
2. Contraction of the uterus
- During pregnancy the number of oxytocin receptors increases as parturition approaches
Positive Feedback Loop
Stimulus: baby sucking the nipples -> suckling sends impulse to your hypothalamus -> produce oxytocin -> secrete in the posterior pituitary ->hypothalamus will signal posterior pituitary to release oxytocin -> oxytocin will be released into the blood stream -> stimulate milk ejection from the mammary gland -> milk is released into the baby
