Lecture 23: Endocrine system

Anterior pituitary: FSH

Stimulates the growth and development of follicles in ovaries and thus the oogenesis (female gamete production)

Stimulates secretion of estrogens (female sex hormone) and stimulates spermatogenesis in males

Not making spermm/oocytes

Anterior pituitary: LH

Completes process of follicle development in ovary that was started by FSH

Once ovulation has occurred, high LH level stimulates cell left behind in the empty follicle to multiply and develop into another endocrine structure → corpus luteum

FSH and LH production → Hypothalamic pituitary gonadal axis

GnRH release in hypothalamus

Causes LH and FSH to be released from anterior pituitary gland

Targets testis and ovaries

Starts producing estrogen, progesterone and testosterone

New hormones produced affects gonadotrophs making LH and FSH higher

FSH in males

Stimulate sertoil cells

Increases spermatogenesis

LH in male

Stimulate Interstitial cells → Leydig cells

Increase release of testosterone

FSH in females

Stimulates Ovary

Increases folliculogenesis

Increases production of estrogen

LH in females

Stimulates ovary

Signals corpus luteum cells

Increases progesterone

Progesterone high to maintain pregnancy

Posterior pituitary

Does not produce any hormones

Stores two hormones produced by hypothalamus

Releases it periodically

Antidiuretic hormone

Oxytocin

Posterior pituitary glands and release of hormones

Hypothalamus sends nerve impulses to nerve endings of posterior pituitary

Releases Oxytocin or ADH into bloodstream

Anterior pituitary → hormones release from hypothalamus through portal vein

ADH

Help body conserve water when short supply in kidney

Causes kidney to reabsorb more water from urine

Goes back into blood stream

Oxytocin in Uterus

Induces contraction by myometrium

Breeding

• Help movement of spermatozoa up to oviducts

Parturition

• Aid delivery and expulsion of placenta

Can be injected to induce birth

Oxytocin in mammary glands

Movement of milk down to lower parts of gland

Circulates down mammary gland

Causes cells around alveoli and small ducts to contract

Oxytocin action on smooth muscle cells of myometrium

Endogenous and exogenous oxytocin promotes myometrium contraction

Activate receptor and its action on voltage regulated Ca²⁺ channels that facilitate Ca influx to cell

Oxytocin activate receptors and Ca receptors work

Prostaglandin (inflammatory mediators) produced

• Actin and Myosin bind causing muscle contractions

Ca important to start contraction on smooth muscle

Major endocrine glands: Anterior pituitary → Thyroid gland

TSH from anterior pituitary → Affect thyroid gland

Two lobes on each side of larynx

Two different cells

• Thyroid follicular epithelium

• Medullary (C) cells

Thyroid gland: Medullary (C) cells

Thyroid gland: Epithelial cells

Thyroid gland producing Thyroid hormones

Anterior pituitary gland releases TSH

TSH activates Thyroid glands

Thyroid glands release T3 and T4

T4

• Converted to T3 in peripheral tissues like liver, kidney, muscle when needed

• Back up for T3

T3

• Most biologically active form of thyroid hormone

T3 and T4: Calorigenic effects

Regulate metabolic rate of cells

Help generate heat and maintain body temperature

T3 and T4: Protein, Carbohydrate and Lipid metabolism

It may induce protein anabolism or catabolism

Depend on energy availability in diet

T3 and T4 levels with heat stress and glucose

Heat stress lower if T3 and T4 levels were normal

Lower glucose won’t make lots of protein

Not enough heat tolerance because low on glucose

Body now needs to break down muscles to make glucose

Lose lots of weight, negative economic effect

Thyroid gland: Calcitonin

Produced by C cells

Located between thyroid follicles

One of two hormones involved in maintaining homeostasis of blood Ca levels (other is parathyroid)

Thyroid gland: Parathyroid gland

Small pale nodules in/on/near thyroid glands

Produce parathyroid hormone (Parathormone)

Help maintain blood Ca homeostasis

Opposite effect of calcitonin

PTH homeostasis

Secreted by parathyroid gland

Increases renal Ca reabsorption (kidney)

Produces 1,25(OH)₂D₃ → Active form of vitamin D

Stimulates Ca absorption by intestinal epithelial

Positive feedback

Calcitonin homeostasis

Secreted by thyroid glands

Lower blood calcium if too high

Inhibit reabsorption of bone Ca

Increases urinary Ca loss

Aims to lower blood concentrations of Ca

Negative feedback

Calcium homeostasis in dairy cows

Parturient paresis (milk fever)

Common disease after calving in dairy cattle

Caused by high demand for Ca when lactating period begins

Result from inability to regulate calcemia

Use lots of Ca for uterus muscles

Lactation also uses lots of Ca for fetus

Calcium homeostasis in dairy cows

During milking

• Have hypocaclemia

• When Ca in blood is lower, calcitonin is lower

• Doesn’t want to get rid of calcium

Low hypocalcemia

• More PTH

• Less Calcitonin

Adrenal glands

Named for their proximity to kidneys

Appears to be single structured, they are two glands

Outer adrenal cortex and inner adrenal medulla

Different structures and functions

Adrenal cortex

Stimulated and controlled by ACTH

Hormone produced by anterior pituitary

Produces three main groups of hormone

• Glucocorticoid hormone

• Mineralocorticoid hormones

• Sex hormones (small amounts)

Adrenal cortex: Glucocorticoid hormones

Cortisol

Cortisone

Corticosterone

Increases blood glucose levels → Hyperglycemic effect

Glucose produced so you don’t faint when stressed

Adrenal cortex: Glucocorticoid hormones

Hypothalamus release CRH

Signals anterior pituitary to release ACTH

ACTH stimulates adrenal cortex

Releases glucocorticoids

Negative feedback

• Cortisol inhibits hypothalamus and pituitary

• Once cortisol is produced, it inhibits glands from releasing hormones