Regulatory mechanisms

in animals

Regulatory pathways

Homeostasis is maintenance of a relatively stable internal environment within an organism

This is achieved through the actions of the nervous system and the hormonal system

These systems have their own function but “cooperate” to maintain homeostasis, this is called chemical communication

Feedback mechanismsA change occurs which affects a key variable which causes the production of a signal

The signal must be detected by receptor

The signal is transferred to a control centre

The control centre sends another signal (to an effector)

An effector (muscle or gland) responds to the signal

The original signal is decreased and the process continues until it is switched off

Negative Feedback System

Along with the Positive Feedback System Regulates homeostasis

Negative feedback systems respond to a stimulus to bring a condition back to normal

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Types of hormones

Those synthesised from fatty acids

Those protein-based hormones

Small and lipid-soluble (what does this mean?)

Water soluble and cannot pass through

membranesMove into cytoplasm and bind to receptors, then pass to nucleus where they act on particular genes

Bind to a specific receptor in the plasma

membrane

Include: testosterone and estrogen

Include: adrenaline and growth hormone

Endocrine Glands

Typically release hormones directly into circulatory system.

The endocrine system is instrumental in regulating metabolism, growth, development and puberty, tissue function, and also plays a part in determining mood.

The Pituitary Gland

• Central role in overall endocrine regulation

• More than half of the hormones in mammals are released from the Pituitary Gland

The Endocrine System

• Controls many body functions– exerts control by

releasing special chemical substances into the blood called hormones

– Hormones affect other endocrine glands or body systems

• Derives its name from the fact that various glands release hormones directly into the blood, which in turn transports the hormones to target tissues via ducts.

The Endocrine System

• Exocrine glands - transport their hormones to target tissues via ducts.

• Endocrine Emergencies:– from common:

• Diabetes

• to the unusual:

– Thyrotoxicosis

The Endocrine System

• Consists of several glands located in various parts of the body.

• Pituitary gland: a small gland located on a stalk hanging from the base of the brain - AKA

• “The Master Gland” – Primary function is to

control other glands.– Produces many

hormones.– Secretion is controlled by

the hypothalamus in the base of the brain.

The Endocrine System

• The Pituitary Gland is divided into 2 areas, which differ– structurally and

functionally – each area has

separate types of hormone production.

• The two segments are:

– Posterior Pituitary:

• produces oxytocin and antidiuretic hormone (ADH)

– Anterior Pituitary:

• produces thyroid-stimulating hormone (TSH)

• growth hormone (GH)

• adrenocorticotropin (ACTH)

• follicle-stimulating hormone (FSH)

The Endocrine System

• And even more…– luteinizing hormone

(LH)

– prolactin

• Let’s go over these one at a time...

• Posterior Pituitary– Oxytocin (the natural

form of pitocin)• stimulates gravid

uterus• causes “let down”

of milk from the breast.

– ADH (vasopressin) causes the kidney to retain water.

The Endocrine System• Anterior Pituitary

– Primarily regulates other endocrine glands

– rarely a factor in endocrinological emergencies

– TSH stimulates the thyroid gland to release its hormones, thus metabolic rate

• Anterior Pituitary…– Growth hormone (GH)

glucose usage consumption of

fats as an energy source

– ACTH stimulates the adrenal cortex to release its hormones

– FSH & LH stimulates maturation & release of eggs from ovary.

The Endocrine System• The Thyroid Gland

– lies in the anterior neck just below the larynyx.

– Two lobes, located on either side of the trachea, connected by a narrow band of tissue called the isthmus.

– Sacs inside the gland contain colloid

• Within the colloid are the thyroid hormones:– thyroxine (T4)– triiodothyronine (T3)

• When stimulated (by TSH or by cold), these are released into the circulatory system and the metabolic rate.

– “C” cells within the thyroid produce the hormone calcitonin.

The Endocrine System

• Calcitonin, when released, lowers the amount of calcium in the blood.

• Inadequate levels of thyroid hormones = hypothyroidism, or Myxedema.

• Myxedema symptoms:

– Facial bloating

– weakness

– cold intolerance

– lethargy

– altered mental status

– oily skin and hair

– TX: replacement of thyroid hormone.

The Endocrine System• Increased thyroid

hormone release causes hyperthyroidism, commonly called Graves’ disease. – Signs and symptoms:

• insomnia, fatigue• tachycardia• hypertension• heat intolerance• weight loss

– Long term hyperthyroidism:

• Exopthalmos– bulging of the

eyeballs (picture Barbara Bush)

• In severe cases - a medical emergency called thyrotoxicosis can result.

The Endocrine System

• Parathyroid Glands– small, pea-shaped

glands, located in the neck near the thyroid

– usually 4 - number can vary

– regulate the level of calcium in the body

– produce parathyroid hormone - level of calcium in blood

– Hypocalcemia can result if parathyroids are removed or destroyed.

The Endocrine System

• Pancreas– a key gland located in

the folds of the duodenum

– has both endocrine and exocrine functions

– secretes several key digestive enzymes

• Islets of Langerhans– specialized tissues in

which the endocrine functions of the pancreas occurs

– include 3 types of cells:• alpha ( )

• beta ()

• delta ()

– each secretes an important hormone.

The Endocrine System

• Alpha () cells release glucagon, essential for controlling blood glucose levels.

• When blood glucose levels fall, cells the amount of glucagon in the blood .

• The surge of glucagon stimulates the liver to release glucose stores (from glycogen and additional storage sites).

• Also, glucagon stimulates the liver to manufacture glucose -

• gluconeogenesis.

The Endocrine System

• Beta Cells () release insulin (antagonistic to glucagon).

• Insulin the rate at which various body cells take up glucose. Thus, insulin lowers the blood glucose level.

• Insulin is rapidly broken down by the liver and must be secreted constantly.

• Delta Cells () produce somatostatin, which inhibits both glucagon and insulin.

The Endocrine System

• Adrenal Glands– 2 small glands that sit

atop both kidneys.

– Each has 2 divisions, each with different functions.

• the Adrenal Medulla secretes the catecholamine hormones norepinephrine and epinephrine (closely related to the sympathetic component of the autonomic nervous system).

The Endocrine System

• The Adrenal Cortex secretes 3 classes of hormones, all steroid hormones:– gluticocorticoids

mineralocorticoids

– androgenic hormones

• One at a time…– gluticocorticoids:– accounts for 95% of

adrenal cortex hormone production

the level of glucose in the blood

– Released in response to stress, injury, or serious infection - like the hormones from the adrenal medulla.

The Endocrine System

• Mineralocorticoids:– work to regulate the

concentration of potassium and sodium in the body.

• Prolonged in adrenal cortex hormone results in Cushing’s Disease.

• Signs & Symptoms of Cushing’s Disease: in blood sugar

levels

– unusual body fat distribution

– rapid mood swings

The Endocrine System

• And - if there is an in mineralocorticoids as well– A serious electolyte

imbalance will occur due to the potassium excretion by the kidney, which results in hypokalemia.

• Sodium can also be retained by the kidney, resulting in hyponatremia.– Causes:

• dysrhythmias• coma• death

– usually results from a tumor - TX? Removal of tumor.

The Endocrine System

• Gonads and Ovaries:– the endocrine glands

associated with human reproduction.

– Female ovaries produce eggs

– Male gonads produce sperm

• both have endocrine functions.

• Ovaries:– located in the

abdominal cavity adjacent to the uterus.

– Under the control of LH and FSH from the anterior pituitary they manufacture

• estrogen

• protesterone

The Endocrine System

• Estrogen and Progesterone have several functions, including sexual development and preparation of the uterus for implantation of the egg.

• Testes:– located in the scrotum

– produce sperm for reproduction

– manufacture testosterone -

• promotes male growth and masculinization

– Controlled by anterior pituitary hormones FSH and LH.

The Endocrine System

• Endocrine Emergencies:

• Diabetes Mellitus– one of the most

common diseases in North America.

insulin secretion by the Beta () cells of the islets of Langerhans in the pancreas.

• Complications of Diabetes:– contributes to heart

disease

– stroke

– kidney disease

– blindness

The Endocrine System

• Pathophysiology of Diabetes:

• Glucose Metabolism– Glucose (dextrose) is a

simple sugar required by the body to produce energy.

– Sugars, or carbohydrates, are 1 of 3 major food sources used by the body.

• The other 2 major food sources are– proteins– fats

• Most sugars in the human diet are complex and must be broken down into simple sugars: glucose, galactose and fructose - before use.

The Endocrine System

• Breakdown of sugars is carried out by enzymes in the gastro intestinal system.– As simple sugars, these

are absorbed from the GE system into the body.

– More than 95% enter the body as glucose.

• To be converted into energy, glucose must first be transmitted through the cell membrane. BUT - the glucose molecule is large and doesn’t readily diffuse through the cell membrane.

The Endocrine System

• Glucose must pass into the cell by binding to a special carrier protein on the cell’s surface. – Facilitated diffusion -

doesn’t use energy. The carrier protein binds with the glucose and carries it into the cell.

• The rate at which glucose can enter the cell is dependent upon insulin levels.– Insulin serves as the

messenger - travels via blood to target tissues.

– Combines with specific insulin receptors on the surface of the cell membrane.