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BIOLOGY MCAT > Chapter five > Flashcards

Chapter five Flashcards

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1
Q

What are peptides?

A

Hormones that are made up of amino acids and range in size. They are derived from larger polypeptides that have cleaved during post-translational modification.

Their effects are usually rapid but short-lived.

They are water soluble, meaning they can travel through the bloodstream and not require carriers.

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2
Q

How do peptides travel?

A

The smaller units are transported to the golgi apparatus for further modifications that activate the hormone and direct them to the correct locations. They are then released by exocytosis.

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3
Q

First v. secondary messenger (peptides)

A

Because peptides are charged and can’t pass through the plasma membrane, they must bind to an extracellular receptor.

The first messenger binds to a receptor and transmissions a second signal. The second signal is the secondary messenger.

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4
Q

Signalling cascade

A

The connection between the hormone at the surface and the effect brought about by the secondary messenger.

At each step, there is the possibility for amplification of signal intensity.

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5
Q

Common second messengers (peptides)

A

Cyclic adenosine monophosphate (cAMP)
Inositol triphosphate
Calcium

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6
Q

What are steroid hormones?

A

They are hormones that are derived from cholesterol and produced by the gonads and adrenal cortex.

Not water-soluble so they have to be carried by messengers.

Effects are slower but longer-lived because they participate in gene regulation.

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7
Q

Steroid hormone receptors

A

Receptors are usually intracellular (cytosol) or intranuclear (in the nucleus). Once bound to the receptor, steroid-hormone complexes undergo conformational changes. One common conformational change is dimerization, the pairing of two receptor-hormone complexes.

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8
Q

Protein carriers for steroid hormones

A

Some of these proteins are very specific and only carry one hormone while others are not so specific. Hormones are inactive while carried and must dissociate from carrier to properly function.

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9
Q

What are amino acid derivative hormones?

A

These are less common and derived from one or two amino acids with a few modifications.

They bind intracellularly.

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10
Q

Example of steroid hormones

A

Estrogen, testosterone

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11
Q

Example of amino acid derivative hormones

A

Includes the epinephrine, norepinephrine, triiodothyronine and thyroxine.

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12
Q

Direct hormones

A

These hormones are secreted and act directly on the target tissue. For example, insulin released by the pancreas causes increased uptake of glucose by muscles.

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13
Q

Tropic hormones

A

These hormones require an intermediary to act
For example, GnRH stimulates the release of LH and FSH. LH acts on the gonads stimulating the release of testosterone and estrogen. GnRH and LH do not cause direct changes in muscles, bone and hair follicles, but they stimulate the production of another hormone that acts on these tissues.

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14
Q

The endocrine organs

A

These organs can synthesize and secrete hormones. It includes the hypothalamus, pituitary, thyroid, parathyroid, adrenal glands, pancreas, gonads, and pineal glands.

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15
Q

Hypothalamus

A

This is the bridge between nervous and endocrine system. It mostly controls the pituitary gland through the release of hormones and has an organism-wide effect.

Release of hormones is regulated by negative feedback, which means the hormone released inhibits the release of other substances.

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16
Q

How does the hypothalamus interact with the anterior pituitary?

A

The hypothalamus releases compounds into the hypophyseal portal system, which is the blood vessel system that connects the hypothalamus and the anterior pituitary. Once the hormones are released, they travel down the pituitary stalk into the anterior pituitary, stimulating the release of other hormones.

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17
Q

The tropic hormones and negative feedback loops of the hypothalamus + anterior pituitary

A

The anterior pituitary secretes many tropic hormones which releases another hormone which has a negative feedback loop

GnRH → FSH + LH

GHRH (growth hormone releasing hormone) → GH (growth hormone)

TRH (thyroid-releasing hormone) → TSH (thyroid stimulating hormone)

CRH (corticotropin-releasing factor) → ACTH (adrenocorticotropic hormone) → releases cortisol → cortisol decreases the release of CRH and ACTH

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18
Q

Three-organ system of hypothalamus and anterior pituitary

A

Called the axes. This includes the hypothalamus, anterior pituitary and the adrenal cortex. In this situation, CRH (corticotropin-releasing factor) → ACTH (adrenocorticotropic hormone) → releases cortisol → cortisol decreases the release of CRH and ACTH

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19
Q

Exception of negative feedback loop in hypothalamus and anterior pituitary

A

The one exception is PIF (prolactin-inhibiting hormone) which is actually dopamine, which is released by the hypothalamus and causes a decrease in prolactin secretion – as long as hypothalamus releases PIF, no prolactin will be released

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20
Q

Hypothalamus interactions with posterior pituitary

A

Neurons in the hypothalamus send axons down pituitary stalk directly into the posterior pituitary, which release oxytocin and antidiuretic hormone.

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21
Q

The hormones released by the anterior pituitary

A

FLAT PEG
FSH
LSH
ACTH
TSH
Prolactin
Endorphins
Growth hormone

FLAT = tropic hormones
PEG = direct hormones

22
Q

Prolactin

A

One of the direct hormones released by the anterior pituitary.

It is more important in females because it stimulates milk production in mammary glands. The release of dopamine decreases the secretion. It is not until the expulsion of the placenta when estrogen, progesterone and dopamine drop, and lactation begins.

23
Q

Endorphins

A

One of the direct hormones released by the anterior pituitary.

Causes a decreased perception of pain (“runners high”) and can induce a sense of euphoria (e.g., heroine)

24
Q

Growth hormones (GH)

A

One of the direct hormones released by the anterior pituitary.

This hormone requires large quantities of glucose. GH prevents glucose uptake in certain tissue and stimulates breakdown of fatty acids

Excess in childhood = gigantism

Deficiency in childhood = dwarfism

In adults, it affects smaller bones only = acromegaly

25
Q

How does milk production work?

A

Nipple stimulation results in oxytocin being released from posterior pituitary (ejection of milk) and prolactin being released from anterior pituitary (milk projection)

26
Q

Posterior pituitary

A

Contains nerve terminals of neurons with cell bodies in the hypothalamus. This does not synthesize any hormones, only releases them.

The two hormones are antidiuretic hormone (ADH) and oxytocin.

27
Q

Antidiuretic hormone

A

Hormone released by the posterior pituitary.

Secreted in response to low blood volume or increase blood osmolarity. Increases permeability of duct to water
Increase reabsorption of water, resulting in greater water retention and increased blood volume/blood pressure.

28
Q

Oxytocin

A

Hormone released by the posterior pituitary.

Allows for smooth muscle contraction (milk production). It may also be connected to bonding behaviour.

Finally, it is the one hormones with a positive feedback loop, meaning that it promotes more oxytocin release.

29
Q

Two major functions of the thyroid

A
  1. Setting basal metabolic rate (by released T3 and T4)
  2. Promoting calcium homeostasis (by releasing calcitonin)
30
Q

Hypothyroidism

A

A deficiency of iodine or inflammation of the thyroid. Not enough thyroid hormones.

Causes lethargy, decreased body temperature, slow respiration, cold intolerance, slow heart rate, weight gain

Deficiency in children will result in intellectual disability and developmental delay, known as cretinism

31
Q

Hyperthyroidism

A

An excess of the thyroid hormone.

Causes heightened activity level, increased body temperature, increased respiratory and heart rate, heat intolerance, and weight loss.

32
Q

Calcitonin

A

Produced by C-cells in the thyroid.

Decreases calcium levels in plasma in three ways: increasing calcium excretion from kidneys, decreasing calcium absorption from gut, and increasing storage of calcium in bone.

33
Q

Parathyroid glands

A

Four small pea-shaped structures that sit on the posterior surface of the thyroid. It secretes parathyroid hormone (PTH).

34
Q

Parathyroid hormone (PTH)

A

Secreted by the parathyroid gland.

It functions antagonistic hormone to calcitonin. The overall effect of PTH – increase in blood calcium with little effect on phosphate (because the absorption of phosphate in the gut and excretion in kidneys cancel each other)

35
Q

Adrenal cortex

A

Secretes corticosteroids, which are steroids that can be divided into glucocorticoids, mineralocorticoids, and cortical sex hormones

36
Q

Glucocorticoids

A

Steroid hormones that regulate glucose and affect protein metabolism.

Includes cortisol and cortisone which raise glucose by increasing gluconeogenesis, decreasing protein synthesis, and decreases inflammation.

Controlled by ACTH

37
Q

Mineralocorticoids

A

Used in salt and water homeostasis with profound effects on the kidneys.

Includes aldosterone which increases sodium reabsorption while not changing osmolarity.

Under the control of renin angiotensin-aldosterone

38
Q

Cortical sex hormones

A

Includes androgens and estrogens

Adrenal testosterone plays a small role in male physiology because the testes secrete large quantities of androgens. On the other hand, females are much more sensitive because ovaries secrete small amounts. Certain enzyme deficiencies in the pathways of these hormones can cause in masculinized genitalia in a female at birth.

Same effect for males with excessive production of estrogens

39
Q

The 3 S’s (function of corticosteroids)

A

Salt
Sugar
Sex

40
Q

Adrenal medulla

A

Inside the adrenal cortex and responsible for production of epinephrine and norepinephrine.

Have system-wide effects centered on the fight or flight response.

Cortisol (long-term) increases synthesis of catecholamines (short-term)

41
Q

The exocrine and endocrine functions of the pancreas

A

Exocrine functions: produces digestive enzymes

Endocrine functions: small clusters of hormone-producing cells are grouped together into islets of Langerhans, which contains alpha, beta, and delta cells

Alpha = glucagon
Beta = insulin
Delta = somatostatin

42
Q

Glucagon

A

Secreted by alpha cells of the pancreas.

Secreted during fasting. For example, when glucose is low, glucagon increases glucose production.

When glucose is high = glucagon release is inhibited

43
Q

Insulin

A

Secreted by beta cells of the pancreas.

Secreted when blood glucose levels are high
Induces muscle and liver cells to uptake glucose and store it for later use.

Stimulates anabolic processes such as fat and protein synthesis.

44
Q

Common issues with insulin

A

Excess insulin = low blood glucose = hypoglycemia

Underproduction of insulin = high blood glucose = hyperglycemia (diabetes)

Excessive glucose will overwhelm kidneys ability to reabsorb glucose, causing an increase in urine production. This explains why diabetes often report increased urination and increased thirst.

45
Q

Type 1 diabetes

A

Insulin-dependent

Caused by autoimmune destruction of beta-cells and this, insulin formation.

These patients require insulin injections to prevent hyperglycemia and permit uptake of glucose in cells.

46
Q

Type 2 diabetes

A

Non-insulin-dependent

This is a result of resistance to insulin, often caused by environmental factors .

These patients only require oral medications. They only require insulin when their bodies can’t control blood glucose, even with the help of medications.

47
Q

Somatostatin

A

Secreted by delta cells of the pancreas.

Inhibitor of insulin and glucagon secretion.

High blood glucose stimulates secretion.

Decreases growth hormone secretion.

48
Q

Pineal gland

A

Secretes melatonin which is involved in circadian rhythm. This gland responds to decreases in light intensity by releasing melatonin.

49
Q

Erythropoietin

A

Kidneys produce erythropoietin, which stimulates bone marrow to increase the production of erythrocytes (red blood cells).

This is secreted in response to low oxygen levels in the blood.

50
Q

Atrial natriuretic peptide (ANP)

A

Heart releases atrial natriuretic peptide (ANP) to regulate salt and water balance. This promotes absorption of sodium and increases urine volume.

BIOLOGY MCAT (3 decks)

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