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Endocrine > Physiology > Flashcards

Physiology Flashcards

1
Q

Define an endocrine system

A

Integrates and controls organ function via secretion of chemicals (hormones) from cells, tissues or glands which are carried to target organs distally via blood.

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2
Q

How do tissues detect hormones?

A

Through presence of specific receptors for that hormone - no receptor, no response.

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3
Q

What is a neuroendocrine system?

A

Combined neural and endocrine system - nerves release hormones which travel in blood to effect distal targets.

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4
Q

What is the general response of insulin in skeletal muscle/adipose tissues?

A

Increased glucose uptake

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5
Q

What is the general response of insulin in liver tissues?

A

Increased glycogenesis

Decreased gluconeogenesis

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6
Q

List features of an endocrine hormone

A
  • Produced by a cell or group of cells
  • Secreted from those cells into the blood
  • Transported via the blood to distant targets
  • Exert their effects at very low concentrations (act in the range 10-9 -10-12 M)
  • Act by binding to receptors on target tissues
  • Have their action terminated, often via negative feedback loops.
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7
Q

What are the three classifications of endocrine hormones?

A
  1. Peptide/protein hormones
  2. Amine hormones
  3. Steroid hormones
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8
Q

How are peptide hormones sythesised?

A

Synthesised as preprohormones, cleaved into prohormones and stored in vesicles along with enzymes to break them down into active hormones

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9
Q

What is the inactive fragment of the insulin prohormone?

A

C-peptide, which is excreted along with active insulin.

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10
Q

What can C-peptide be used to demonstrate clinically?

A

Can be used to indicate endogenous insulin production from the pancreas (though is usually about 5x higher than insulin)

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11
Q

Are peptide hormones water/fat soluble?

A

Water soluble - can transport easily in blood but can not cross cell membrane

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12
Q

What signalling pathways do peptide hormones use?

A

Most work via GPCR or tyrosine kinase linked pathways

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13
Q

List some examples of peptide hormones

A

TRH
FSH
Insulin

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14
Q

Are amine hormones water/fat soluble?

A

Yes.

Catecholamines - Water soluble (like peptides)

Thyroid hormones - Fat soluble (like steroids)

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15
Q

What amino acid are most amine hormones derived from?

A

Tyrosine

(With the exception of melatonin, derived from tryptophan).

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16
Q

List some amine hormones

A

Dopamine, Norepinephrine, Epinephrine, Thyroxine (T4), Triiodothyronine (T3)

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17
Q

How are steroid hormones synthesised?

A

Directly as needed, not stored.

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18
Q

Are steroid hormones water/fat soluble?

A

Fat soluble - cant be retained within lipid membranes.

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19
Q

How are steroid hormones transported?

A

Via carrier proteins in blood. (eg albumin, or more specific like corticosteroid-binding globulin)

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20
Q

List four organs that produce steroid hormones?

A

Gonads - sex steroids,
Placenta - hCG, sex streroids,
Kidney - Vitamin D3,
Adrenal cortex - corticosteroids

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21
Q

What structure are all steroid hormones derived from?

A

Cholesterol

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22
Q

What is the mechanism of action of steroid hormones?

A

Intracellular receptors - alter gene expression - increase/decrease protein synthesis.

(Occasionally bind to cell surface receptors)

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23
Q

How do steroid hormones reach their targets?

A

Only unbound hormone can diffuse across capillary walls to target cells.

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24
Q

What has the longer half-life? Steroids or peptide hormones?

A

Steroids - hours to days

Peptides - minutes

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25
Q

How is hormone secretion regulated?

A

In most pathways, through negative feedback reflexes.

Also neural feedback loops

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26
Q

What happens to receptor number with prolonged high concentration of hormone?

A

Downregulation of receptor number

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27
Q

What happens to receptor number with prolonged low concentration of hormone?

A

Upregulation of receptor number

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28
Q

Give an example of a permissive hormone effect?

A

Epinephrine and thyroid hormone leads to greater fatty acid release than epinephrine alone

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29
Q

Give an example of a antagonistic hormone effect?

A

Growth hormone impairs the response to insulin by decreasing insulin receptor number

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30
Q

What connects the pituitary gland to the hypothalamus?

A

The infundibulum

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31
Q

What is the endocrine function of the hypothalamus?

A

Integration centre for endocrine systems

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32
Q

What type of tissue is posterior pituitary?

A

Neural tissue

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33
Q

What type of tissue is anterior pituitary?

A

Endocrine, of epithelial origin

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34
Q

What are some functions of the hypothalamus?

A 
Puberty,
Pregnancy, 
Breastfeeding,
Sleep,
Menstrual Cycle,
Day/Night,
Exercise,
Hydration Status,
Metabolic Demand,
Stress,
Cold
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35
Q

What are some functions of the pituitary?

A 
Metabolism,
Water balance,
Growth,
Parturition, 
Lactation,
Gonadal Function,
Thyroid Function,
Adrenal Function
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36
Q

What is a tropic hormone?

A

A hormone that governs the release of other hormones

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37
Q

What are the hypothalamic tropic hormones?

A

Thyrotropin Releasing Hormone (TRH)
Corticotropin Releasing Hormone (CRH)
Growth Hormone Releasing Hormone (GHRH)
Gonadotropin Releasing Hormone (GnRH)
Prolactin Releasing Hormone (PRH)
Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
Dopamine aka Prolactin Inhibiting Hormone (PIH)

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38
Q

Where are hormones released from in the hypothalamus?

A

Median eminence

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39
Q

How much of the pituitary is the anterior?

A

2/3rds of the gland

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40
Q

How is the anterior pituitary connected to the hypothalamus?

A

Through the capillary portal system

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41
Q

What controls the production of anterior pituitary hormones?

A

Hypothalamus

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42
Q

What category of hormones are released from the anterior pituitary?

A

Peptide hormones

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43
Q

What are the anterior pituitary hormones?

A
  • Thyroid Stimulating Hormone (TSH) aka thyrotropin
  • Adrenocorticotrophic Hormone (ACTH) aka corticotropin
  • Follicle Stimulating Hormone (FSH)
  • Luteinising Hormone (LH)
  • Growth Hormone (GH)
  • Prolactin
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44
Q

What is short-loop feedback?

A

Feedback from hormones produced by pituitary to hypothalamus.

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45
Q

What is long-loop feedback?

A

Feedback from endocrine target cells to earlier stages in the pathway

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46
Q

What hormones are released by posterior pituitary?

A

Vasopressin (ADH)

Oxytocin

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47
Q

Where are posterior pituitary hormones synthesised?

A

The hypothalamus

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48
Q

What is the main function of vasopressin?

A

Regulation of water balance

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49
Q

What is the main function of oxytocin?

A

Milk Ejection and Uterine contraction

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50
Q

What is hyposecretion?

A

Too little hormone secretion

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51
Q

What is hypersecretion?

A

Too much hormone secretion

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52
Q

What is hyporesponsiveness?

A

Reduced response of target cells

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53
Q

What is hyperresponsiveness?

A

Increased response of target cells

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54
Q

What is a primary endocrine disorder?

A

A disorder in which the defect is in the cells that secrete the hormone - ie hypothyroidism caused by too little thryoxine production

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55
Q

What is a secondary endocrine disorder?

A

A disorder in which the defect is in too much/too little trophic hormone produced by the pituitary - ie hypothyroidism caused by too little TSH production

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56
Q

What is a tertiary endocrine disorder?

A

A disorder in which the defect is in the hypothalamus - ie hypothyroidism caused by too little TRH production

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57
Q

What are the two centres within the hypothalamus responsible for balancing energy intake?

A

Feeding Centre

Satiety Centre

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58
Q

What is the glucostatic theory of energy balance?

A

Food intake (and drive to eat) is determined by blood glucose. Satiety centres sensitive to insulin.

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59
Q

What is the lipostatic theory of energy balance?

A

Food intake (and drive to eat) is determined by fat stores. Driven by leptin (released by fat stores and suppresses feeding).

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60
Q

What are the three components of metabolism?

A
  1. Extracting energy from nutrients in food
  2. Storing energy
  3. Utilising energy for work
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61
Q

What does the brain use for energy?

A

Glucose

Except in starvation - ketones

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62
Q

What is the normal range of blood glucose?

A
  1. 2-6.3mM

* THINK 5 mM*

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63
Q

What do α cells produce in the islets of Langerhans?

A

Glucagon

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64
Q

What do β cells produce in the islets of Langerhans?

A

Insulin

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65
Q

What do δ cells produce in the islets of Langerhans?

A

Somatostatin

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66
Q

What do F cells produce in the islets of Langerhans?

A

Pancreatic polypeptide

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67
Q

What does insulin do to nutrients?

A

^Glucose oxidation
^Glycogen synthesis
^Fat synthesis
^Protein synthesis

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68
Q

What does glucagon do to nutrients?

A

^Glycogenolysis
^Gluconeogenesis
^Ketogenesis

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69
Q

What is the major stimulus of insulin secretion?

A

Blood glucose concentration

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70
Q

What is the only hormone that lowers blood glucose?

A

Insulin!

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71
Q

What does insulin bind to?

A

Tyrosine kinase receptors in insulin-sensitive tissues.

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72
Q

What transporter is recruited by insulin?

A

GLUT-4 glucose transporter

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73
Q

What tissues require insulin to take up glucose?

A

Muscle and fat - insulin dependant

74
Q

What does insulin do in the liver?

A

Activates hexokinase - converts glucose to G-6-P, and therefore maintains a concentration gradient to pull glucose into the cell

75
Q

What are the additional actions of insulin?

A
  • Increase glycogen synthesis
  • Increases amino acid uptake
  • Increases protein synthesis
  • Increases triacylglycerol synthesis
  • Inhibit the enzymes of gluconeogenesis
  • Permissive effect on Growth Hormone
  • Promotes K- ion entry into cells by stimulating Na+/K+
76
Q

What is a hormone released by fat stores which depresses feeding activity?

A

Leptin

77
Q

What organ gets priority access to glucose?

A

Brain - obligate glucose user! (But doesnt require insulin)

78
Q

Approximately what percentage of the pancreas has endocrine function?

A

1%

79
Q

Where is excess glucose stored?

A

Glycogen in liver and muscle

TAG in liver and adipose tissue

80
Q

What controls the release of insulin from beta-cells?

A

Glucose enters - ATP binds to K-ATP channel - no K release (remains in cell) > Depolarisation -> Calcium channels open - trigger insulin vesicle release

81
Q

How does liver uptake glucose?

A

Through GLUT 2 transporters

82
Q

What stimulus increase insulin release?

A
  1. Increased [BG]*
  2. Increased [amino acids]plasma
  3. Glucagon (insulin required to take up glucose created via gluconeogenesis stimulated by glucagon)
  4. Other (incretin) hormones controlling GI secretion and motility eg gastrin, secretin, CCK, GLP-1, GIP.
  5. Vagal nerve activity
83
Q

What stimulus inhibits insulin release?

A
  1. Low [BG]
  2. Somatostatin (GHIH)
  3. Sympathetic alpha 2 effects
  4. Stress e.g. hypoxia
84
Q

What is greater - the insulin response to an IV administration of glucose or an oral administration of glucose?

A

An oral administration of clucose -^ inuslin by direct effect of glucose on beta cells + vagal stimulation, + incretin effects (other hormones from gut)!

Oral leading - anticipatory effects

85
Q

Where does glucagon mainly act?

A

On the liver (Is a glucose-mobilising hormone)

86
Q

What hormones form part of the glucose counter-regulatory control system, (oppose the actions of insulin)?

A

Glucagon
Epinephrine
Cortisol
GH

(In all of these, glucose release is needed!)

87
Q

What kind of receptors are glucagon receptors?

A

G-protein coupled receptors - linked to cAMP

88
Q

What actions does glucagon have?

A
  1. Increased glycogenolysis
  2. Increased gluconeogenesis (substrates: aa’s and glycerol (lipolysis))
  3. Formation of ketones from fatty acids (lipolysis

(Net result is more [BG]!)

89
Q

What do amino acids in plasma do glucagon levels?

A

Increase glucagon release

90
Q

What do amino acids in plasma do insulin levels?

A

Increase insulin release

91
Q

Why do amino acids in plasma raise glucagon levels (along with insulin)?

A

To compensate for very protein heavy meals with little carbohydrate - since amino acids increase levels of insulin, blood glucose would fall.

Glucagon release counteracts this.

92
Q

In the post-absoprtive state, what is the benefit of having less insulin release?

A

Glucose in plasma is free to be used for obligate glucose users (ie the brain), and isn’t taken up by muscle/fat.

93
Q

What stimuli promote glucagon release?

A
  1. Low [BG]
  2. High [amino acids] . Prevents hypoglycaemia
    following insulin release in response to aa.
  3. Sympathetic innervation and epinephrine,
    beta2 effect
  4. Cortisol
  5. Stress e.g. exercise, infection
94
Q

What stimuli inhibit glucagon release?

A
  1. Glucose
  2. Free fatty acids and Ketones
  3. Insulin (Falls in diabetes so glucagon levels rise despite high [BG])
  4. Somatostatin
95
Q

What glucose regulating hormone is secreted in response to parasympathetic activity of the vagus?

A

^Insulin

^Glucagon to lesser extent -anticipatory

96
Q

What glucose regulating hormone is secreted in response to sympathetic activity?

A

^Glucagon,
^Epinephrine

\/ Insulin

(Promote glucose mobilisation - think fight or flight!)

97
Q

What effects does epinephrine have on [BG]?

A

^Muscle glycogenolysis
^Liver glycogenolysis
^Lipolysis

98
Q

What effects does cortisol have on [BG]?

A

^Gluconeogenesis
^Inhibition of glucose uptake
^Lipolysis
^Protein catabolism

99
Q

What effects does growth hormone have on [BG]?

A

^Gluconeogenesis
^Inhibition of glucose uptake
^Lipolysis

100
Q

Where is somatostatin secreted from?

A

D-cells of pancreas

And hypothalamus - GHIH

101
Q

What are the actions of somatostatin?

A
  • Inhibit activity in GI tract
  • -Suppresses release of both insulin and glucagon
  • Inhibits secretion of GH from anterior pituitary
102
Q

What happens to the entry of glucose into skeletal muscle in exercise?

A

Glucose entry increases

GLUT4 transporters can migrate without insulin in exercise!

103
Q

What does exercise do to insulin sensitivoty of muscle?

A

Increases it

104
Q

What does the brain adapt to use as energy in starvation?

A

Ketones

105
Q

What is ketone uptake dependent on?

A

Insulin!

If not enough insulin (eg type 1 diabetes) Ketone build up leads to life-theatening acidosis!

106
Q

What factors regulate growth?

A
  • Growth hormone release from anterior pituitary – which in turn is regulated by the balance of GHRH vs GHIH release from the hypothalamus
  • Thyroid hormones
  • Insulin
  • Sex steroids (esp. at puberty)
  • Availability of nutrients
  • Stress
  • Genetics
107
Q

Where is somatotropin released from?

A

Anterior pituitary (Growth hormone!)

108
Q

What is the action of somatostatin on growth hormone?

A

Inhibits its effects

Growth hormone inhibiting hormone!

109
Q

What actions does growth hormone have?

A

Indirectly - growth and development

Directly - regulation of metabolism

110
Q

What hormones does growth hormone require permissive action of before growth can be stimulated?

A

Thyroid hormones
Insulin

(Impaired growth in hypothyroidism/uncontrolled diabetes?

111
Q

At what stage of life does growth hormone secretion cease?

A

It doesn’t. GH secretion continues throughout life - essential for maintenance and repair

112
Q

How does GH stimulate growth in tissues?

A

Stimulate cell size (hypertrophy)

Stimulate cell division (hyperplasia)

113
Q

What mediates the action of growth hormone?

A

Insulin-like growth factor (IGF-1)/Somatomedin C

114
Q

What kind of effect does IGF-1 have on glucose?

A

Promotes hypoglycaemia - glucose uptake in muscle (similar to insulin)

115
Q

What tissue secretes IGF-1?

A

Liver

116
Q

How are GH and IGF-1 transported in the blood?

A

Via carrier proteins.

117
Q

What feedback does IGF-1 exert on GH?

A

Negative feedback - inhibits GHRH and stimulated GHIH

GH also limits own feedback

118
Q

What effects does GH/IGF-1 have on bone growth?

A
  • Stimulate chondrocyte precursor into chondrocytes

- Cells produce IGF-1 - auto/paracrine singalling to trigger cell division and production of cartilage

119
Q

What do sex steroids do to bone growth?

A

Close epiphyseal plates - no further growth

120
Q

What effects does GH have on metabolism?

A

^Gluconeogenesis
^Inhibition of glucose uptake
^Lipolysis

^Amino acid uptake and protein synthesis in almost all cells

(The first 3 allows for more development of brain etc!)

121
Q

At what stage of life is highest rates of GH secretion seen?

A

Teenage years

122
Q

At what stage of the day is GH secretion the highest?

A

First 2 hours of sleep

123
Q

What stimuli increase GHRH secretion?

A
  • Actual or potential \/ in energy supply to cells (exercise, cold)
  • ^Amino acids in plasma
  • Stressful stimuli
  • Delta sleep
  • Oestrogen and progesterone
124
Q

What stimuli increase GHIH secretion?

A
  • Glucose
  • FFA
  • REM sleep
  • Cortisol
125
Q

What hormones affect growth?

A 
GH
IGF-1
Thyroid hormones
Sex steroids (Puberty)
Glucocorticoids
Insulin
126
Q

What are the two periods of rapid growth in humans?

A

Infancy

Puberty

127
Q

What may cause dwarfism?

A
  • Deficiency of GHRH
  • Abnormal GH secreting cells
  • End Organ unresponsiveness
  • Genetic mutations
  • Precocious puberty
  • Hypothyroidism
128
Q

What roles does calcium play in the body?

A
  • Signalling
  • Blood Clotting
  • Apoptosis
  • Skeletal Strength
  • Membrane Excitability
129
Q

Where is 99% of calcium stored?

A

Bones (Mostly as hydroxyapatite)

130
Q

How is extracellular calcium stored?

A

40% bound to plasma proteins (Albumin, globulin)
10% bound to anions

50% physiologically active

131
Q

What happens to calcium binding in alkalotic conditions?

A

Binding capacity increases - may precipitate hypocalcaemia.

132
Q

What takes precedece - bone function as mechanical support or maintaining Ca2+ balance?

A

Maintaining Ca2+ takes precedence - think demineralisation is osteomalacia etc

133
Q

What are the bone building cells which lay down the collagen ECM to be calcified?

A

Osteoblasts

134
Q

What do osteoblasts differentiate into?

A

Osteocytes

135
Q

What cells are responsible for mobilizing bone - break down the ECM?

A

Osteoclasts

136
Q

What two hormones act to ^ [Ca2+] in plasma?

A 
Parathyroid hormone (PTH)
Calcitriol (Active form of Vitamin D3)  - produced by liver and kidneys
137
Q

How does PTH increase free [Ca2+] in plasma?

A
  • Stimulating osteoclasts to ^resorption
  • Inhibit osteoblasts to reduce ca2+ depostion
  • Increase Ca2+ reabsorption from kidneys (Decrease excretion from urine)
  • Increase renal excretion of phosphate
  • Stimulate kidney to synthesise calcitriol
138
Q

Why does increasing renal excretion of phosphate increase free [Ca2+] in plasma?

A

Prevents calcium being deposited in bone - this requires phosphate

139
Q

Why does calcitriol increase free [Ca2+] in plasma?

A

Promotes calcium absorption at gut and kidney

140
Q

How is calcitriol formed?

A

From vitamin D/Precursors activated by sunlight on skin

Stimulated by prolactin

141
Q

What happens in increasing plasma levels of calcium?

A

Inhibition of PTH

142
Q

What are the actions of calcitriol?

A
  • Increase absorption of Ca2+ from the gut.
  • Facilitates renal absorption of Ca2+
  • Mobilises calcium stores in bone by stimulating osteoclast activity.
143
Q

What hormone acts to decrease [Ca2+]?

A

Calcitonin

144
Q

Where is calcitonin secreted from?

A

Thyroid gland

145
Q

What are the actions of calcitonin?

A

Bind to osteoclasts and inhibit bone resorption

^Renal excretion

(But less important in humans!)

146
Q

What other hormones increase plasma [Ca2+]?

A

Increase -

Cortisol,
Insulin,
Oestrogen,
Prolactin

147
Q

What other hormone leads to decrease plasma [Ca2+]?

A

Growth Hormone

148
Q

What does the adrenal medulla secrete?

A

Catecholamines

Epinephrine, Norepinephrine and dopamine

149
Q

What is the adrenal medulla derived from embryologically?

A

Neural crest tissue

150
Q

What does the adrenal medulla secrete?

A 
Mineralcorticoids (Aldosterone)
Glucocorticoids (Cortisol)
Sex steroids (Testosterone)
151
Q

What zone of the adrenal cortex secretes aldosterone?

A

Zona glomerulosa

152
Q

What zone of the adrenal cortex secretes glucocorticoids?

A

Zona fasciculata

153
Q

What zone of the adrenal cortex secretes sex hormones?

A

Zona reticularis

154
Q

What are all steroid hormones derived from?

A

Cholesterol

155
Q

What is the adrenal cortex derived from embryologically??

A

Mesoderm

156
Q

What is the long-loop feedback pathway of cortisol?

A

Cortisol inhibiting anterior pituitary secretion (ACTH secretion) and hypothalamic secretion (CRH)

157
Q

What aspect of metabolism do glucocorticoids influence (Cortisol)?

A

Cortisol - Influences Glucose metabolism

Permissive effect on glucagon - increases blood glucose!

158
Q

When is cortisol release generally at its peak in circadian rhythm?

A

6-9am

159
Q

What are the actions of cotisol on glucose metabolism?

A
  • Stimulates gluconeogenesis
  • Proteolysis (to provide gluconeogenic substrates)
  • Lipolysis
  • Decreased insulin sensitivity
160
Q

What are the effects of cortisol on ca2+ balance?

A

Decreases Ca2+ absorbtion on the gut, increases secretion.

Can also increase bone resorption -> osteoporosis

161
Q

List some other actions of cortisol?

A
  • Impairment of mood/cognition
  • Permissive effects on norepinephrine (-> hypertension etc)
  • Suppression of immune system
162
Q

What are the functions of aldosterone?

A

-Stimulates Na+ retention and K+ depletion, resulting in increased blood volume and ^BP^

163
Q

What does an decrease of aldosterone do to blood pressure?

A

Decreased aldosterone -> Decreased BP

164
Q

What promotes CRH/ACTH release?

A

Stress/Alcohol/Caffeine/Lack of sleep -> All contribute to raised cortisol levels - vulnerability to infection.

165
Q

What are the two hormones produced by the thyroid?

A

Triiodothyronine (T3)

Thyroxine (T4)

166
Q

In the thyroid, what do C (clear) cells secrete?

A

Calcitonin (Ca2+ regulating hormone)

167
Q

In the thyroid, what cells support thyroid hormone synthesis?

A

Follicular cells

168
Q

What is the large protein rich in tyrosine residues from which thyroid hormones are manufactured?

A

Thyroglobulin

169
Q

How is iodide actively concentrated from the plasma into follicular cells?

A

Through a Na/I symport transporter.

170
Q

How is iodide transported into the colloid?

A

Via the pendrin transporter

171
Q

What enzyme catalyses the addition of iodide to tyrosine residues on the thyroglobulin molecule?

A

Thyroid peroxidase

172
Q

What hormone influences release of TH into the plasma?

A

TSH

173
Q

Which thyroid hormone is predominant in the plasma?

A

T4 (thyroxine)

174
Q

Which thyroid hormone is more physiologically active

A

T3 (triiodothyronine)

175
Q

How is T4 converted to T3?

A

Deiodinase enzymes

176
Q

What hormones are inhibitory to TSH?

A

Glucocorticoids

Somatostatin

177
Q

List functions of thyroid hormones?

A
  • Raise metabolic rate and promote thermogenesis (through futile metabolism cycles)
  • Increase hepatic gluconeogenesis (but no effect on BG if insulin is released)
  • Net increase in proteolysis
  • Net increase in lipolysis
  • Critical for growth (Stimulates GH receptor expression)
  • Essential for brain development)
178
Q

What is contained in the colloid of the thyroid?

A

Thyroglobulin

179
Q

What hormone triggers TSH release from the pituitary?

A

TRH (Thyroid releasing hormone)

180
Q

What causes an increase in PTH?

A

A fall in serum [calcium]

181
Q

What are the functions of PTH?

A

Promote reabsoprtion of calcium from renal tubules and bone

Mediate conversion of inactive vitamin D to calcitriol.

Increase renal excretion of phosphate

Endocrine (4 decks)

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