BS530: 6.2 Hypothalamus and Pituitary Glands

What connects the hypothalamus to the pituitary gland?

The infundibulum

What are the two functions of the hypothalamus?

Neural and endocrine functions

How does the hypothalamus act as part of the nervous system?

Its neurons send and receive messages from other neurons

How does the hypothalamus act as part of the endocrine system?

Its neurons release hormones into the bloodstream

What are the two major lobes of the pituitary gland?

Anterior pituitary and posterior pituitary

What is another name for the posterior pituitary?

Neurohypophysis

What is another name for the anterior pituitary?

Adenohypophysis

What type of tissue makes up the posterior pituitary?

Neural tissue

What type of tissue makes up the anterior pituitary?

Glandular epithelial tissue

How many major hormones does the pituitary secrete?

At least eight major hormones

What structure connects the hypothalamus and posterior pituitary?

Hypothalamic-hypophyseal tract

Which hypothalamic nuclei produce oxytocin?

Paraventricular nuclei

Which hypothalamic nuclei produce ADH?

Supraoptic nuclei

Where are oxytocin and ADH stored before release?

Axon terminals in the posterior pituitary

What triggers release of posterior pituitary hormones?

Firing of hypothalamic neurons

What are the two hormones secreted by the posterior pituitary?

Oxytocin and ADH

What type of hormones are oxytocin and ADH?

Peptide hormones

How many amino acids are in oxytocin and ADH?

Nine amino acids

What is another name for ADH?

Vasopressin

Where is ADH formed?

Supraoptic nuclei of the hypothalamus

What stimulates ADH release?

High osmolarity or low blood pressure

What receptors monitor osmolarity for ADH release?

Osmoreceptors in the hypothalamus

What organs does ADH act on?

Kidneys and blood vessels

How does ADH affect the kidneys?

Increases aquaporins and water reabsorption

What effect does high ADH concentration have on blood vessels?

Vasoconstriction

What is the overall effect of ADH on blood pressure?

Increases blood pressure

What inhibits ADH release?

Alcohol and diuretics

What receptor mediates ADH vasoconstriction?

AVPR1 receptor

What second messenger system does AVPR1 use?

PLC-IP3 pathway

Where are AVPR2 receptors located?

Basolateral membrane of collecting ducts

What second messenger system does AVPR2 use?

cAMP pathway

What does activation of AVPR2 cause?

Insertion of aquaporin 2 channels and water reabsorption

What is diabetes insipidus?

A disorder caused by deficient ADH activity leading to excessive dilute urine

What are the two types of diabetes insipidus?

Central and nephrogenic

What causes central diabetes insipidus?

Low ADH production

What causes nephrogenic diabetes insipidus?

Kidneys not responding to ADH

What is a major symptom of diabetes insipidus?

Polyuria

Why can diabetes insipidus cause dehydration?

Excessive water loss through urine

What medication is used to treat central diabetes insipidus?

Desmopressin

How does urine osmolarity change after desmopressin in central DI?

It increases

How does urine osmolarity change after desmopressin in nephrogenic DI?

No significant change

What happens to ADH levels in nephrogenic DI?

They are elevated

What is SIADH?

Syndrome of inappropriate ADH secretion

What happens to ADH levels in SIADH?

They are excessively high

What are common causes of SIADH?

Head trauma tumors CNS disorders infections and drugs

How does SIADH affect plasma osmolarity?

Decreases plasma osmolarity

How does SIADH affect plasma sodium?

Causes hyponatremia

How does SIADH affect urine volume?

Decreases urine volume

How does SIADH affect urine osmolarity?

Increases urine osmolarity

What are symptoms of SIADH?

Fluid retention headache and disorientation

What severe complication can occur in SIADH?

Seizures coma or death from hyponatremia

How is SIADH treated?

Fluid restriction saline vasopressin antagonists and diuretics

How does diabetes insipidus affect urine volume?

Increases urine volume

How does diabetes insipidus affect urine osmolarity?

Decreases urine osmolarity

How does diabetes insipidus affect plasma sodium?

Causes hypernatremia

What urine dipstick finding is common in diabetes insipidus?

Low specific gravity

Where is oxytocin formed?

Paraventricular nuclei of the hypothalamus

What stimulates oxytocin release during labor?

Pressure of the baby's head on the cervix

What stimulates oxytocin release during breastfeeding?

Nipple stimulation

What cells send signals to the hypothalamus during oxytocin release?

Mechanoreceptors

What organs does oxytocin act on?

Breast myoepithelial cells and uterus

What type of feedback regulates oxytocin?

Positive feedback

What second messenger system does oxytocin use?

PIP2-calcium system

What are the major actions of oxytocin?

Milk ejection and uterine contractions

What behavioral effects are associated with oxytocin?

Bonding trust and nurturing

Why is the anterior pituitary called the master gland?

Its hormones stimulate other endocrine glands

How does the hypothalamus control the anterior pituitary?

Through releasing and inhibiting hormones in the hypophyseal portal system

What vessels make up the hypophyseal portal system?

Primary capillary plexus portal veins and secondary capillary plexus

Is there a direct neural connection to the anterior pituitary?

No

What embryologic tissue gives rise to the anterior pituitary?

Oral ectoderm

Why is the posterior pituitary called the neurohypophysis?

Because it develops from neural tissue

Why is the anterior pituitary called the adenohypophysis?

Because it develops from glandular tissue

List the six anterior pituitary hormones.

GH ACTH TSH PRL FSH LH

What type of hormones are all anterior pituitary hormones?

Peptide hormones

Which anterior pituitary hormone is both tropic and non-tropic?

Growth hormone

Which anterior pituitary hormone is non-tropic only?

Prolactin

Which anterior pituitary hormones are tropic hormones?

TSH ACTH FSH LH and GH

What cells secrete growth hormone?

Somatotropes

What cells secrete ACTH?

Corticotropes

What cells secrete TSH?

Thyrotropes

What cells secrete FSH and LH?

Gonadotropes

What cells secrete prolactin?

Lactotropes

What hypothalamic hormone stimulates TSH release?

TRH

What hypothalamic hormone stimulates LH and FSH release?

GnRH

What hypothalamic hormone stimulates ACTH release?

CRH

What hypothalamic hormone stimulates GH release?

GHRH

What hypothalamic hormone inhibits GH release?

Somatostatin

What hypothalamic hormone inhibits prolactin release?

PIH dopamine

What stimuli can activate the hypothalamus?

Pain smell emotions nutrients electrolytes water and hormones

What is another name for growth hormone?

Somatotropin

What type of receptor does GH use?

Enzyme-linked receptor

What are the two major effects of GH?

Metabolic and anabolic effects

What stimulates GH release?

GHRH

What inhibits GH release?

Somatostatin and negative feedback

How does GH affect blood glucose?

Raises blood glucose

How does GH affect gluconeogenesis?

Increases gluconeogenesis

How does GH affect glucose uptake by cells?

Decreases glucose uptake

How does GH affect fat metabolism?

Increases lipolysis and fatty acid release

How does GH affect protein metabolism?

Increases amino acid uptake and protein synthesis

Why is GH considered diabetogenic?

It causes insulin resistance and hyperglycemia