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Notes 4.1.3 - Hormonesa. Key definitions:

a. Endocrine gland – a gland that secretes hormones directly into the blood without the use of ducts.

i. E.g. Islets of Langerhan.b. Exocrine gland – a gland that secretes molecules into a duct where

they’re carried to target tissue/cells.i. E.g. sweat glands.

c. Hormone – a molecule released into the blood by an endocrine gland; it acts as a messenger.

i. E.g. glycogon.d. Target Tissue – possesses specific complementary receptors on the

membrane.i. E.g. liver cells.

b. First and second messenger (adrenalin and cyclic AMP):a. Adrenalin cannot enter the target cell and therefore must cause effects

in the cell from outside the cell. The adrenalin receptor on the membrane of the cell is complimentary to the adrenalin molecule, the first messenger and is associated with the enzyme: edenyl cyclase.

i. First messenger transmits signals around the body.b. After binding to the receptor, the enzyme edenyl cyclase is activated –

this converts ATP to cyclic AMP (cAMP), the secondary messenger. The cAMP causes effects inside the cell.

i. Second messenger transmits signals inside the cell.

c. Functions of the adrenal glands:a. Located above both kidneys – divided into the

cortex and medulla (manufactures and releases adrenaline due to shock, pain, etc. This has widespread effects because many cells have adrenalin receptors).

i. Functions:1. Relax smooth muscle in the bronchioles.2. Increase stroke volume of heart.3. Increase heart rate.4. Vasoconstriction -> higher blood pressure.5. Glycogenolysis.6. Pupil dilation.7. Increased mental awareness.8. Inhibited gut action.9. Body hair to stand on end.

b. Adrenal cortex (creates steroid hormones using cholesterol):i. The mineralocorticoids (controls sodium and potassium levels in

blood).ii. The glucocorticoids help maintain metabolism of carbohydrates of

protein in the liver.

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d. The pancreas is a small organ lying below the stomach – it has both endocrine and exocrine glands.

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a. Exocrine gland:i. Cells found in small groups surrounding tiny tubules (into which

they secrete their enzymes). Tubules join to form the pancreatic duct (which carries the fluid to the small intestine). It contains:

1. Amylase – a carbohydrase.2. Lipase.3. Trypsinogen – an inactive protease.

b. Endocrine gland:i. Certain areas of the pancreas called the Islets of Langerhans

(endocrine function) contain different types of cells.1. Alpha – manufacture and release of glucagon.2. Beta – manufacture and release of insulin.

ii. These are released directly into the blood stream.e. Regulation of blood glucose with insulin and glucagon:

a. If the blood glucose level is too high:i. The beta cells (part of the Islets of Langerhan) detect the level is

too high and secrete insulin into the bloodstream to lower the blood glucose level. Insulin has several effects on cells:

1. More glucose channels are placed in the cell surface membrane.

a. More glucose enters cells.b. The glucose in the cells is converted into glycogen

(glycogenesis).2. More glucose is converted to fats and is used in respiration.

b. If the blood glucose level is too low:i. The alpha cells detect the change and secrete the hormone

glucagon into the bloodstream to raise the blood glucose level. The effects are:

1. Conversation of glycogen to glucose (glycogenolysis).2. Use of more fatty acids in respiration.3. Production of glucose from amino acids and fats

(gluconeogenesis).c. This is known as negative feedback.

f. Controlling the secretion of insulin (with the use of potassium and calcium channels):

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g. Causes of diabetes:a. Type-1 (insulin-dependent):

i. Starts in childhood and is thought to be the result of an auto-immune attack (destroying the beta cells).

b. Type-2 (non-insulin-dependent):i. Develops later in life particular if someone is: obese, has a bad

diet, has a family history of diabetes or is Asian of afro-Caribbean. Can still produce insulin but the body doesn’t respond to it is less strong.

h. Treatment of diabetes:a. Type-1:

i. Insulin injections:1. Source: extraction from animal pancreas, genetically

engineered (which is better because: faster acting and more effective insulin, less chance of developing a tolerance to the insulin, less chance of immune rejection, lower risk of infection, cheaper, more adaptable manufacture (to demand) and less moral objections).

ii. Stem cells:1. Scientists have recently found precursor cells in the

pancreas of adult mice – these are capable of developing into a variety of different cells (stem cells). If similar cells are found in humans, they may be able to turn into beta cells.

b. Type-2:i. Diet control:

1. Take care in matching carbohydrate intake and output.i. The heart must adapt to the level of activity the body is doing.

a. Some of the changes that could occur include:i. Heart rate.ii. Strength of contractions.iii. Stroke volume.

b. Control of the heart rate:i. The heart muscle is myogenic.ii. The SAN is the hearts own ‘pacemaker’. The SAN is a region of

conductive tissue located above the atria walls. It releases a wave of excitation causing contractions over the atria. This causes the AVN to release a new wave down the Purkyne fibers and causes the ventricles to contract.

iii. Nerves from the medulla oblongata (controls the unconscious functioning of the body (i.e. breathing rate…) supply the heart – these nerves connect to the SAN. Though they don’t initiate the contractions, they control the frequency of contractions.

1. Action potentials sent down the accelerator nerve increase the heart rate.

2. Action potentials sent down the vagus nerve reduce the heart rate.

iv. The heart muscle responds to adrenalin.c. Interaction between control mechanisms:

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i. Resting heart rate is maintained by the SAN, which has a set frequency (varying from person to person). The frequency can be controlled by the cardiovascular center in the medulla oblongata.

ii. Factors that control the heart rate:1. Stretch receptors in the muscles send impulses to the

cardiovascular center informing it that extra oxygen may be required and this usually increases the heart rate.

2. When we exercise the concentration of carbon dioxide in blood increases (lowering the PH). This is detected by chemoreceptors in the carotid arteries, the aorta and the brain. These also send impulses to the cardiovascular center (which increases the heart rate).

a. When we stop exercising, the concentration of carbon dioxide falls and the activity of the accelerator nerve reduces, resulting in a slower heart rate.

3. Adrenalin is secreted in response to shock, pain, stress, and excitement… The presence of adrenaline in the blood increases the heart rate, helping the body prepare for activity.

iii. Artificial pacemakers:1. A device that delivers an electrical impulse to the heart

muscle. Some pacemakers are used just to replace the AVN (if the SAN is working fine).