2. Hypothalamus and Pituitary Gland

Pituitary Gland

• Located just beneath the hypothalamus, connected by a thin stalk known as the infundibulum

Anterior Lobe (Front):

• Connected to the hypothalamus by blood vessels

• Some cells may produce more than one hormone

• Controlled by releasing factors and inhibiting factors secreted from the hypothalamus, into the blood

Anterior Lobe - Hormones

• Thyroid Stimulating Hormone (TSH)

• Prolactin (PRL)

• Follicle Stimulating Hormone (FSH)

• Luteinising Hormone (LH)

• Adrenocorticotropic Hormone (ACTH)

• Growth Hormone (GH)

Posterior Lobe (Back)

• Connected to the hypothalamus by nerve fibres

• The cell bodies from which these fibred connect are located in the hypothalamus

• Secretory materials synthesized in cell bodies in the hypothalamus are transported down axons and stored in the posterior lobe

Posterior Lobe - Hormones

• Oxytocin (OT)

• Anti - Diuretic Hormone (ADH)

Thyroid Stimulating Hormone (TSH)

Target:

• Thyroid Gland

Major Actions in Humans:

• Stimulates synthesis and secretion of thyroid hormones

Prolactin (PRL)

Target:

• Mammary Glands

Major Actions in Humans:

• Promotes milk secretion and mammary growth

Follicle Stimulating Hormone (FSH)

Target:

• Females: Ovaries

• Males: Testes

Major Actions in Humans:

• Females: stimulates the growth of follicle and oestrogen secretion

• Males: stimulates the growth and maturation of sperm and testosterone secretion

Luteinising Hormone (LH)

Target:

• Females: Ovaries

• Males: Testes

Major Actions in Humans:

• Females: - Stimulates ovulation of ripe follicle and formation of corpus luteum

• Males: Stimulates interstitial cells of the testes to synthesise and secrete testosterone

Adrenocorticotropic Hormone (ACTH)

Target:

Adrenal Cortex

Major Actions in Humans:

Promotes synthesis and secretion of adrenal cortical hormones

Growth Hormone (GH)

Target:

Most Tissues

Major Actions in Humans:

• Promotes growth in stature and mass

Oxytocin (OT)

Target:

Mammary Glands and Uterus

Major Actions in Humans:

• Induces milk movements into secretory ducts of the breasts for breast feeding

• Induces uterine contractions during childbirth

Anti - Diuretic Hormone (ADH)

Target:

• Targets kidneys

Major Actions in Humans:

• Helps maintain water balance in the body. ADH increases the amount of water reabsorption by the kidneys (opens pores to allow more water to be absorbed)

What hormones does the thyroid gland secrete?

• Triiodothyronine (T3)

• Thyroxine (T4)

• Calcitonin

T3 and T4

T3 and T4:

• Controls metabolism and synthesis of molecules

• Increases absorption of glucose from small intestine to the blood

• Increases cellular respiration, which increases rate of glucose absorption into body cells

Effect: Release of energy (heat maintains body temperature)

Stimulated by TSH

Amount:

80% Thyroxine (T4)

20% Triiodothyronine (T3)

Thyroxine (T4) is less active but lasts longer than Triiodothyronine (T3)

Calcitonin

• Lowers blood calcium levels by supressing osteoclast activity in the bones

• Increases calcium excreted in the urine

• Decreases calcium uptake in the intestine

What does parathyroid gland secete?

• Parathyroid Hormone (PTH)

Parathyroid Hormone

• Controls blood calcium and phosphate levels

• Stimulated by TSH

Pancreas (Exocrine and Endocrine Glands):

• Exocrine: Digestive enzymes secreted into small intestine, through the pancreatic duct

• Endocrine: Islets of Langerhans: Cells that secrete insulin and glucagon

Pancreas - Insulin Secretion Process

Effect: controls blood sugar levels

• Insulin (produced by beta cells in the Islet of Langerhans)

• Glucose → Glycogen & Fat (Blood Sugar Levels ↓)

Pancreas - Glucagon Secretion Process

Effect: controls blood sugar levels

• Glucagon (produced by alpha cells in the Islet of Langerhans)

• Glycogen & Fat → Glucagon (Blood Sugar Levels ↑)

Testes

• Testes secrete Androgens (inc testosterone)

• Effect: Development & Maintenance of male features

Ovaries:

• Ovaries secrete oestrogen and progesterone

• Effect: Development and maintenance of female features, regulate the menstrual cycle and changes during pregnancy

Pineal Gland

• Secretes melatonin

• Effect: Regulation of sleep patterns

• Stimulated by darkness and inhibited by light

Adrenal Medulla

• Secretes adrenaline (epinephrine)

• Effect: flight or fight response (stimulation)

• Secretes noradrenaline (norepinephrine)

• Effect: fight or flight response (stimulation) and specifically ↑ HR and force

Adrenal Cortex

• Secretes corticosteroids (20 hormones)

• E.g: Cortisol and Aldosterone

• Effect: Cortisol promotes metabolism, helps withstand stress and helps repair damaged tissue

• Effect: Aldosterone acts on the kidneys to ↑ potassium and ↓ sodium in the urine

Thymus

• Secretes thymosin

• EFfect: maturation of t lymphoctyes ( t cells)

• Shrinis afters puberty

Endocrine Tissue

• Stomach and small intestine secrete hormones which coordinate exocrine glands of the digestive system

• Kidneys secrete erythropoietin (EPO), a hormone that stimulates RBC production on bone marrow

• Heart secretes hormones to reduce BP

• Placenta secretes hormones to maintain pregnancy, stimulate foetal growth, and stimulate mammary glands