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Biomedicine I > 9. Endocrine System > Flashcards

9. Endocrine System Flashcards

1
Q

Endocrine System

A

• The endocrine system coordinates the activity of organs through hormones -chemical messengers released into the blood from glands which produce them. • Hormones have specific target cells,some far from where the hormone is produced, others effect cells of the same organ where they were released, or the same cell.

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2
Q

Types of Hormones

A
  1. P eptides(proteins –water soluble): i.e. Insulin. 2. Steroids: sex hormones 3. Amino acid derivatives: adrenaline, thyroxine
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3
Q

Types of Glands

A

Exocrine Endocrine

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4
Q

Exocrine

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• Excrete products into ducts leading to body cavities/organ/skin. • Examples: Salivary glands (saliva), Gastric glands (digestive enzymes), Mammary glands.

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5
Q

Endocrine

A

• Ductless, secreting hormones directly into the blood. • Examples: Pituitary, Adrenals, Thyroid.

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6
Q

Endocrine Glands

A

• Hypothalamus (neuroendocrine gland) • Pituitary (glandular & neuroendocrine) • Pineal • Thyroid • Parathyroid • Adrenal • Pancreatic: islets of Langerhans • Thymus • Ovaries • Testes

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7
Q

Endocrine Tissues

A

Some tissues of the body are not considered glands but have endocrine function (produce hormones)

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8
Q

Adipose Tissue

A

Leptin (suppresses food intake) & resistin(blood glucose)

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9
Q

Heart

A

Atrial natriuretic peptide (blood pressure)

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10
Q

GIT

A

Stomach -ghrelin & gastrin (satiety & gastric emptying)

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11
Q

Liver

A

Angiotensinogen, Insulin-like growth factor (IGF), thrombopoietin.

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12
Q

Placenta

A

Human chorionic gonadotropin (hCG) & progesterone

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13
Q

Kidneys

A

Erythropoietin (RBC production) & calcitriol (Vit. D).

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14
Q

Skin

A

Cholecalciferol (Vit D)

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15
Q

Hormone Activity: Receptors

A

• Hormones have specific target cells. • They influence the activity of the target cells by binding to specific receptors. • The receptors for protein based hormones are part of the cell membrane, whilst lipid hormone receptors are within the cell. • Receptors can be made up of a number of different proteins. • Receptors allow hormones to have a stimulating or inhibitory effect on different cell-types.

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16
Q

Down-regulation

A

• If a hormone is present in excess,the number of target cell receptors may decrease. • Example: Hormone increase during puberty. Negative Feedback

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17
Q

Up-Regulation

A

• A deficiency in hormone causing an increase in the number of receptors on target cells. • Example:Increased number of oxytocin receptors in third trimester of pregnancy Positve feedback

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18
Q

Hormone Regulation

A

Hormone secretions are regulated by: 1. Nervous system signals. 2. Chemical changes in the blood. 3. Other hormones. • Hormones interact to allow maximum flexibility in response to the environment. • They are controlled through positive and negative feedback loops.

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19
Q

Endocrine System Control

A

• The pituitary gland is often named the ‘master endocrine gland’ as it controls many of the other endocrine glands in the body. It is itself regulated (signalled) by the hypothalamus. • The pituitary gland has an anterior and posterior region. • The hypothalamus & pituitary glands represent the major link between Nervous and Endocrine systems. • Together control almost entirely: Growth, development, metabolism & homeostasis.

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20
Q

Releasing Hormones

A

Thyroid releasing hormone (TRH) Growth hormone releasing hormone (GHRH) Corticotropin releasing hormone (CRH) Prolactin releasing hormone (PRH) Gonadotropin releasing hormone (GnRH)

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21
Q

Inhibiting Hormones

A

Growth hormon inhibiting hormone (GHIH) Prolactin inhibiting hormone - Dopamine (PIH)

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22
Q

Pituitary Gland: Anterior

A

• Receives 7 hormones in capillaries from hypothalamus. • Synthesises& releases: 1. Growth hormone (hGH) 2. Thyroid stimulating hormone (TSH) 3. Follicle stimulating hormone (FSH) 4. Luteinizing hormone (LH) 5. Prolactin (PRL) 6. Adrenocorticotropic hormone (ACTH) 7. Melanocyte stimulating hormone (MSH)

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23
Q

Pituitary Gland: Posterior

A

• Hormones are synthesisedin the hypothalamus. • Receives nerve impulses from the hypothalamus. • Releases these hormones: • Oxytocin • Antidiuretic hormone (ADH)

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24
Q

Anterior Pituitary Hormones

A
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25
Q

Growth Hormone

A

ACTIVITY:
1. Regulates metabolismin many organs.
2. Stimulates release of insulin-like growth factors (IGF’s) in cells.
3. Promotes growth & division of most body cells (especially bone & muscle).
4. Breaks down fats and glycogen.
INCREASED PRODUCTION:
• Night time (sleep –stage 3,4).
• Hypoglycaemia.
• Exercise.
• Childhood & adolescence.

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26
Q

Thyroid Stimulating Hormone (TSH)

A

ACTIVITY:
1. Growth & activity of the thyroid gland: Increasing thyroid hormone production -thyroxine (T4) & tri-iodothyronine (T3).
PRODUCTION:
• Lowest levels in the early evening & highest during the night.

27
Q

Adrenocorticotropic Hormone (ACTH)

A

ACTIVITY:
1. Output of steroid hormones: glucocorticoids, especially cortisol.
2. Circadian rhythm (sleep / wake cycle).
INCREASED PRODUCTION:
• Hypoglycaemia.
• Exercise.
• Stressors such as emotions, fever.
• Interleukin-1 (inflammatory response to infection).
PRODUCTION:
• Highest in the morning and lowest at midnight.

28
Q

Prolactin (PRL)

A

ACTIVITY:
1. Stimulates lactation: prolactin + oxytocin = lactation.
2. Prevents pregnancy during lactation(inhibits GnRH).
3. Breast maturationafter childbirth. Maturationof mammary glands in pregnancy.
PRODUCTION:
• After birth (delivery of placenta).
• Suckling: more milk removed the more produced.
• Emotional stress.
• Sleep.

29
Q

Follicle Stimulating Hormone (FSH) & Luteinizing Hormone (LH)

A
  • FSH:
  • Production of gametes (sex cells) in males and females.
  • Increase oestrogen production (F).
  • Stimulate testosterone production (M).
  • LH
  • Triggers ovulation & formation of the ‘corpus luteum’ in females.
  • Increase secretion of progesterone(F).
  • Stimulates secretion of testosterone(M).
30
Q

Melanocyte Stimulating Hormone (MSH)

A
  • Produced by the anterior pituitary in response to UV light.
  • Stimulated by ‘Corticotropin Releasing Hormone’ (CRH) –released from hypothalamus. So MSH and ACTH share the same precursor molecule.
  • Role in skin, hair and eye pigmentation in humans.
  • Can be excessively produced as part of some pathologies, such as the hyperpigmentation of skin seen in Addison’s disease.
31
Q

Oxytocin

POSTERIOR PITUITARY

A

ACTIVITY:
1. Contracts uterus in childbirth (parturition).
2. Contracts lactating breast.
3. Bonding hormone (mother with baby): Social bonding, trust, skin contact, “cuddle hormone”.
PRODUCTION:
• Suckling.
• Childbirth (positive feedback).
• Emotional state: Fear or anxiety may inhibitrelease of oxytocin or milk let-down. Emotions can trigger oxytocin –just hearing baby’s cry can start lactation!

  • 2 weeks before birth, the baby descends to the bottom of the uterus (womb).
  • The head engages with the wall of the cervix.
  • Sensory neurons act as pressure receptors and when stretched send signals to hypothalamus.
  • Oxytocin is released into bloodstream.
  • Oxytocin causes more forceful contraction of the uterus.
  • Baby’s head engages head of cervix /pressure receptors …. positive feed-forward cycle that builds up momentum.
32
Q

Lactation

A

• It takes 2-3 days for milk production to begin.
• The first breast fluid produced is called ‘colostrum’, which contains water, lacto-sugar and antibodies.
• Colostrum acts as a laxative to encourage a bowel movement. This
is important to remove bilirubin and wastes that have accumulated in the
foetal intestines.

33
Q

Antidiurectic Hormone (ADH)

POSTERIOR PITUITARY

A

• Hypothalamus monitors concentration of body fluid.
ACTIVITY:
1. Reduces urine output by stimulating reabsorption of water in the kidneys.
2. Vasoconstrictionin skin & abdominal organs to increase blood pressure
PRODUCTION:
• Increased osmotic pressure, hypovolaemia(reduced fluid intake, thirst, vomiting).
INHIBITION:
• Reduced osmotic pressure, increased fluid intake, alcohol.

34
Q

Pineal Gland: Melatonin

A
  • The pineal gland is a small pea-sized gland in the midline of the brain that produces melatonin.
  • Specialised photoreceptors in the retina detect light/darkness cues.
  • Levels are highest in children & decline with age.
  • Stimulated by: night, darkness (retinal feedback).
  • Reduced by: daylight, irregular sleep patterns (jetlag, night-shifts).
35
Q

Pineal Gland: Activity

A
  • Contributes to the setting of the circadian rhythm:metabolic, physiological and behavioural alterations that follow a 24 hour rhythm.
  • A potent antioxidant, DNA protective.
36
Q

Thymus Gland

A
  • The thymus is a bi-lobed gland located behind the sternum which plays an important role in immune development.
  • The thymus atrophies after puberty and is replaced by fibrous tissue.
37
Q

‘Thymosin’

A

ACTIVITY:
• Hormones produced by the thymus promote the maturation of T-Lymphocytes.
• Immature T-cells migrate from the red bone marrow to the cortex of the thymus. Mature T-lymphocytes then migrate to the lymphatic system.

38
Q

Thyroid Gland

A
  • A butterfly shaped gland that is inferior to the larynx & located either side of the trachea.
  • Influences metabolic rate (catabolic + anabolic) and is an important ‘growth hormone’ in early life.
39
Q

Thyroid Hormones

A
  • ‘Follicular cells’ produce thyroid hormones
    • Thyroxine (T4) -has 4 iodine atoms.
    • Triiodothyronine (T3) -has 3 iodine atoms.
  • T4 & T3are synthesised from tyrosine & iodine from a specialised thyroid protein called thyroglobulin (Tg).
  • Follicular cells ‘trap’ & store most of the bodies iodide via active transport from blood to cytosol.
40
Q

Thyroid Gland Histology

A
  • Thyroid follicular cells trap and store iodine.
  • Parafollicular cells (lie between follicles) secrete the hormone calcitonin, which functions to lower blood calcium levels.
  • The follicles are filled with a fluid known as‘colloid’ that contains thyroglobulin
41
Q

Thyroid Hormones: Thyroxine and Triiodothyronine

A
  • The major form of thyroid hormone in the blood is thyroxine (ratio of T4 to T3 is approx. 20:1).
  • Selenium - containing enzymes are used in the conversion of T4 to T3. Zinc is also needed for this.
  • T3 is the more biologically active form: 3-4 times more potent than T4.
  • This allows the body to maintain a stable pool of thyroid hormones from which the active, free hormones can be released as required.
  • Thyroid hormone levels is measured in terms of free T4 & T3.
  • Most body cells have receptors for thyroid hormones.
42
Q

Thyroid Hormones: Activity

A
  • Increase metabolic rate & heat production.
  • Essential for normal growth and development and CNS function.
  • Works in conjunction with adrenaline & noradrenaline, insulin & growth hormone.
43
Q

Thyroid Hormones: Production

A
  • Stimulated by:TSH, exercise, stress, malnutrition, low blood glucose, low T3 to T4.
  • Reduced by: low TSH, high T3
  • Highest levels at night
  • Higher levels during adolescence, pregnancy & female reproductive years.
44
Q

Thyroid Hormones: Lab Testing

A
  1. TSH Levels (measure in the morning as it is the highest and most reliable / consistent value).
  2. Free T3 & T4 -unbound form of thyroid hormones are more bioavailableto target cells & tissues.
  3. Thyroglobulin (‘Tg’) -levels in the blood can be used as atumour marker for certain kinds ofthyroid cancer.
  4. Anti-thyroglobulin antibodies(‘TgAb’) -often found in patients with autoimmune thyroid disease (Hashimoto’s or Graves’).
45
Q

Thyroid Gland: Calcitonin

A

• Produced by the parafollicular cells of the thyroid gland.
• Important during childhood for bone growth.
• Lowers blood calcium by:
1. Inhibiting calcium reabsorption from the bone & kidneys.
2. Inhibiting osteoclast activity(opposes parathyroid).
PRODUCTION:
• Stimulated by: increased blood calcium levels.
• Inhibited by: reduced blood calcium levels.

46
Q

Parathyroid Glands

A
  • The parathyroid glands consist of four small glands.
  • They are partially embedded in the posterior surface of the lateral lobes of the thyroid.
  • Produces parathyroid hormones.
47
Q

Parathyroid Hormone (PTH)

A

• Parathyroid hormone increases blood calcium by:
1. Increasing osteoclast activity.
2. Increasing kidney reabsorption of calcium & magnesium.
3. Increasing production of calcitriol which increases calcium absorption in the GIT.
• PTH release is stimulated by reduced blood calcium levels and inhibited by increased blood calcium levels.
• Calcium is essential for muscle contraction, nerve transmission, blood clotting.

48
Q

Adrenal Glands

A

• The adrenals are paired glands superior to the kidneys. Divided into the:

  1. Medulla
  2. Cortex
49
Q

Adrenal Gland: Medulla

A

Medulla(inner): part of the autonomic NS, producing:
• Adrenaline (epinephrine).
• Noradrenaline (norepinephrine).
• Dopamine.

50
Q

Adrenal Gland: Cortex

A

Cortex(outer): produces 3 groups of steroid hormones:
• Glucocorticoids(primarily cortisol).
• Mineralocorticoids (primarily aldosterone).
• Sex hormones (primarily androgens).

51
Q

Adrenaline and Noradrenaline

A
  • Adrenaline (80%) & noradrenaline (20%) are produced by the adrenal medulla.
  • They both intensify the sympathetic response.
  • Released by chromaffin cells (quick release because innervated directly by sympathetic NS).
  • Adrenaline has greater influence on the heart. Noradrenaline effects blood vessels.
  • Stimulated by: Exercise, fasting, shock, elevated temperature, infection, disease, emotional stress, caffeine.
  • Inhibited by: Eating, sleeping, calmness, diaphragmatic breathing.
52
Q

Adrenaline & Noradrenaline Effects

A
  1. Heart: Increases heart rate & contraction causing an increase in blood pressure.
  2. Vessels: Vasodilation in heart, brain, skeletal muscles. Vasoconstriction in digestive tract.
  3. Thyroid: Increases metabolism.
  4. Skeletal muscle/Liver: Increases blood glucose & triglycerides (for metabolism)
  5. Nervous system: Dilate pupils.
53
Q

Glucocorticoids

A
  • Steroid hormones produced in the adrenal cortex which regulate metabolism & resistance to stress.
  • This is mostly ‘Cortisol’.
54
Q

Glucocorticoids: Activity

A
  1. Stimulating gluconeogenesis (new glucose)
  2. Proteolysis (amino acids from protein).
  3. Lipolysis.
  4. Production of glucose by the liver.
  5. Reduces immune response (and tissue repair).
  6. Anti-inflammatory –hence therapeutic use of steroids.
  7. Weak reabsorption of sodium & water from kidney tubules.
55
Q

Mineralocorticoids

A

Primarily ‘aldosterone’ -maintains water & electrolyte balance.

56
Q

Mineralocorticoids: Activity

A
  1. Reabsorption of sodium in kidneys.
  2. Causes retention of water in the kidneys to increase blood volume and blood pressure.
  3. Excretion of potassium in urine.
  4. Promotes excretion of H+ions (acid).
    • Stimulated by: decreased BP or blood volume (dehydration, haemorrhage) and high blood potassium stimulates the ‘renin-angiotensin-aldosterone pathway’.
    • Inhibited by: low blood potassium.
57
Q

Sex Hormones

A

Primarily androgens in the form of dehydroepiandrosterone (DHEA).

58
Q

Sex Hormones: Activity

A
  1. Production of pubic & axillary hair.
  2. Growth: increases muscle mass.
  3. Converted to testosterone then oestrogen (in females -> promotes libido).
  4. Involved in T4 -> T3conversion.
59
Q

Sex Hormones: Production

A
  • Stimulated by CRH -> ACTH
  • Cortical androgens are insignificant compared to amount produced in the ovaries & testes during puberty and adulthood.
60
Q

Pancreas

A
  • The pancreas has both an endocrine & exocrine function.
  • Endocrine function is via the cells called the islets of Langerhans.

• Main endocrine function of the pancreas is to regulate blood glucose levels & maintain within normal range (4-7mmol/L).

61
Q

Types of Endrocrine Cells

A
  1. Alpha cells: produce ‘glucagon’.
  2. Beta cells: produce ‘insulin’.
  3. Delta cells: produce ‘somatostatin’ (GHIH)
62
Q

Pancreas: Insulin

A

• Lowers blood glucose levels, amino acids & fatty acids by:
1. Stimulating cells to up-take glucose from blood.
2. Promoting synthesis of proteins, glycogen (glycogenesis) & fats (lipogenesis).
Stimulated by:
• Directly: high blood glucose, elevated blood amino acids, eating, sweet taste (including artificial sweeteners). Indirectly:GH and ACTH acting to elevate blood sugar levels.
Reduced by:
• Low blood glucose, starvation, glucagon.

63
Q

Pancreas: Glucagon

A

• Acts on the liver to elevate blood glucose levels.
• Converts glycogen to glucose in liver and skeletal muscle (‘glycogenolysis’).
• Gluconeogenesis from lactic acid and amino acids.
• Lipolysis to break down stored fat for use for metabolism.
PRODUCTION:
• Stimulated by: low blood sugar, exercise, stress (fight-or-flight).
• Reduced by: insulin, hyperglycaemia.

64
Q
A

Biomedicine I (18 decks)

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