Hypothalamus and Pituitary Gland

Outline the hypothalamus

• roles in both the nervous and endocrine systems (serves as a connection between the 2 systems)

• regulates many basic functions

  • e.g. body temp., water balance + heart rate, increase/decrease secretions of other glands

• located at base of the brain (below the thalamus and above the pituitary gland)

• size of an almond

• many of its functions carried out through the pituitary gland:

  • hypothalamus secretes releasing factors which stimulates the release of inhibiting factors which slow down secretion of a hormone, these factors travel through blood vessels to anterior lobe of the pituitary gland, affecting secretion of its hormones

  • other hormones are produced by the hypothalamus and pass along nerve fibres to posterior lobe of the pituitary gland then released

What are some basic functions the hypothalamus regulate?

• body temp., water balance + heart rate, increase/decrease secretions of other glands

Outline the pituitary gland

• lies under the hypothalamus, joined by a stalk (infundibulum)

• ~13mm in diameter

• vital to normal functioning of the body

• consists of the anterior and posterior lobes (function seperately):

  • Anterior lobe (front), has no nerves connecting it to the hypothalamus, connecting by a complex network of blood vessels in infundibulum

  • posterior lobe (rear), nerve fibres from nerve cell bodies in hypothalamus pass through infindulum to lobe (directly connected to hyptohalamus), does not produce substances only stores and releases hormones

Outline the anterior lobe

• releases hormones that regulate a range of body activities

• secretions controlled by realising and inhibited factors secreted by the hypothalamus

• anterior lobe of the pituitary gland (front)

What are some hormones secreted by the anterior lobe?

• Gonadotropins - follicle-stimulating hormone (FSH) and Luteinising hormone (LH)

• Gowth Hormone (GH), or somatotropin - stimulates body growth (skeleton, organs)

• Thyroid-stimulating hormone (TSH) - stimulates production and release hormones thyriod gland

• Adrenocorticotropic (ACTH) - controls production and release some hormones from cortex of adrenal glands)

• Prolactin (PRL) - initates and maintains milk production in females (with other hormones)

Outline the posterior lobe

• does NOT produce hormones, only stores and releases

• releases oxytocin and antidiuretic hormone

  • produced in special nerve cells in the hypothalamus, cells have long extensions that pass through the infundibulum to the lobe, hormones manufactured in these cells move through the extensions and are stored in the lobe for release into the bloodstream,

  • release is triggered by nerve impulses iniated in the hypothalamus and conducted along cell extensions

What does Oxytocin do?

• stimulates contaction of the muscles of the uterus

• released in large quantities during labour

• also stimulates contraction of cells in the mammary glands, resulting in release of milk during breastfeeding

What does Antiduiretic hormone do?

• causes the kidneys to remove water from urine that is froming (helps retain fluid in the body)

  • water is returned to the bloodstream

• at high concentrations causes constriction of small arteries

What does Follicle-stimulating hormone do?

Male: Production of sperm

Female: Growth of follicles

What does Luteinising hormone do?

Male: secretion of testosterone

Female: ovulation and maintenance of corpus luteum

Outline the pineal gland

• found deep inside the brain

• size of a pea in children

• after puberty it gradually decreases in size

• secretes melatonin

  • production stimulated by darkness, inhibited by light

What is melatonin for?

• involved in the regulation of sleep patterns

Outline the thyroid gland

• located in the neck, blow the larynx

• consists of 2 lobes, lie on either side of trachea, joined by narrow piece of tissue that lies across the front of the trachea

• contains the follicular cells and C-cells

What do the follicular cells do?

• found in the thyroid

• secrete thyroxine and triiodothyronine in response to thyroid stimulating hormone

What does thyroxine do?

• controls body metabolism

  • regulates reactions where complex molecules broken down to release energy and other reactions where complex molecules are synthesised to simpler ones

• overall effect to bring release of energy and maintain body temperature (some energy released in the form of heat)

What do C-cells do?

• secrete calcitonin

• helps regulate levels of calcium and phosphate in the blood

• if concentration of calcium in blood increases, calcitonin is released

  • reduces the reabsorption of calcium by the kidneys and the breakdown of bone

• if concentration of phosphate in blood increases, calcitonin is released

  • acts to move phosphate into bone and reduces its reabsorption by the kidneys

Outline the parathyroid glands

• located in rear surface of the lobes of the thyroid gland

• usually 4 parathyroid glands (some people have more)

  • each are the size of a small pea

• secrete parathyroid hormone (PTH)

  • increases calcium levels in blood, increases phosphate excretion in urine

Outline the thymus

• located in the chest just above the heart and behind the sternum

• largest in infants and children (shrinks after puberty)

• secretes groups of hormones called thymosins

  • influence maturation of T-lymphocytes (disease-fighting cells)

Outline the adrenal glands (not including regulation of blood sugar hormones)

• 2 adrenal glands, 1 above each kidney

• each adrenal gland has an inner adrenal medulla and outer adrenal cortex

  • essentially 2 seperate endocrine glands within each adrenal gland (very different in structure and function)

What does the adrenal medulla produce? (not including regulation of blood sugar hormones)

adrenaline (epinephrine) and noradrenaline

What does adrenaline (epinephrine) do?

• Has effect similar to that of sympathetic division of autonomic nervous sytem

  • helps prepare body for reaction to a threatening situtation (fight-or-flight response)

What does noradrenaline do?

• has effects similar to adrenaline (epinephrine)

  • increases the rate and force of the heartbeat

Outline the adrenal cortex

• produces corticosteroids → collective of more than 20 different hormones

• two main ones: aldosterone and cortisol

What does aldosterone do?

• acts on the kidney to reduce the amount of sodium and increase the amount of potassium in urine

What does cortisol do?

• with related hormones, promotes normal metabolsim, helping body to withstand stress and to repair damaged tissues

Outline the pancreas

• soft organ

• ~15cm long

• lies below the stomach alongside duodenum, first part of the small intestine

• endocrine and exocrine gland

  • exocrine part secretes digestive enzymes into small intestine through pancreatic duct

  • endocrine part made up of islets of Langerhans

What is secreted by the islets of Langerhans?

• insulin secreted by beta cells in the islets of Langerhans

  • reduces amount of glucose in the bloodstream by promoting uptake of glucose from the blood into the cells of the body, conversion of glucose to glycogen and fat in the liver, formation of glucogen from glucose in skeletal muscles, glucose converted into fat in fat storage tissue, controlled by a negative feedback loop

• glucagon secreted by alpha cells of islets of Langerhans

  • increases blood glucose level, promotes breakdown of glucogen to glucose in liver, also stimulates breakdown of fat in liver and in fat storage tissues

Outline the gonads

• testes and ovaries

• production of sperm and eggs

• produce androgens and oestrogens and progesterone

What are andorgens?

• male sex hormones

• responsible for development and maintenance of male sex characteristics, produced by testes (e.g. testerone)

• females also produce very low levels in the ovaries, adrenal glands and fat cells

What are oestrogens and progesterone?

• female sex hormones

• produced by the overies

• stimulate development and maintenance of female sex characteristics

• regulate menstrual cycle and involved in changes during pregnancy (together with gonadotropic hormones of the pituitary)

What is a hormone the kidneys secrete?

Erythropoetin (EPO) - a hormone that stimulates the production of red blood cells in the bone marrow

Why does the placenta secrete hormones?

Helps maintain the pregnancy, stimulates development of the foetus and stimulates the mother’s mammary glands

Why does the heart secrete a hormone?

To help reduce blood pressure

Why does the stomach and small intestine secrete hormones?

Hormnes coordinate the exocrine glands of the digestive system