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MRCEM Primary > Physiology > Flashcards

Physiology Flashcards

1
Q

Where is the swallowing centre located?

A

Medulla and Pons

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2
Q

What are the 3 stages of swallowing?

A

Buccal (voluntary)
Pharyngeal (involuntary)
Oesophageal (involuntary)

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3
Q

Describe the buccal phase of swallowing

A

Tongue movements push the food bolus towards the hard palate forcing it into the pharynx

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4
Q

Describe the pharyngeal phase of swallowing

A

The food bolus stimulates mechanoreceptors in the pharynx and fires impulses via the afferent branches of the glossopharyngeal (IX) and vagus (X) nerves:
1. Soft palate elevates closing off the nasopharynx
2. Laryngeal muscles contract to close the glottis and elevate the larynx to close the airway
3. Breathing is inhibited
4. The epiglottis moves over the tracheal opening closing off the airway
5. The pharyngeal constrictor muscles contract moving the bolus down
6. The upper oesophageal sphincter relaxes

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5
Q

Describe the oesophageal phase of swallowing and state which nerve is involved

A

Vagus Nerve

Wave of coordinated relaxation and contraction of the circular and longitudinal muscles in the oesophagus

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6
Q

Which are the fat soluble vitamins?

A

A, D, E, K

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7
Q

What are the water soluble vitamins?

A

B, C

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8
Q

Where are fat soluble vitamins stored?

A

Fatty tissue in the body, mainly the liver

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9
Q

Vitamin A deficiency leads to what clinically?

A

Blindness

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10
Q

Vitamin B1 is also known as what? What clinical implication does a deficiency in it have?

A

Thiamine

Beriberi and Wernicke-Korsakoff

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11
Q

Where are osmoreceptors located (control water intake)

A

Anterior Hypothalamus

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12
Q

Where is ADH synthesised and stored?

A

Synthesis: Hypothalamus
Storage: Posterior pituitary

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13
Q

What is the action of ADH?

A
  1. Binds V2 receptors on the principle cells of the late distal tubule and collecting ducts
  2. Insertion of aquaporin channels
  3. Greater water reabsorption and increased concentration of urine

Also acts on V1 receptors causing vascular vasoconstriction

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14
Q

What stimulates the release of ADH?

A

Raised plasma osmolality detected by osmoreceptors in the anterior hypothalamus

(Also: Angiontensin II, pain, nausea, hypoglycaemia)

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15
Q

What does the following result in clincially:
a) ADH deficiency
b) ADH excess

A

a) diabetes insipidus
b) SIADH

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16
Q

Where is CCK released from?

A

I-cells in the duodenum and jejunum

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17
Q

What stimulates and inhibits CCK release?

A

Stimulated: the presence of fatty and amino acids in the duodenum

Inhibited: Somatostatin

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18
Q

What is the role of CCK?

A

Increases production of bile

+ Increases pancreatic bicarbonate secretion
+ Increases pancreatic enzyme secretion
+ Inhibits gastric emptying
+ Inhibits gastric acid production
+ Stimulates pepsinogen secretion

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19
Q

ANP is released in response to what? Where is it released from?

A
  • Atrial stretch
  • Cardiac atrial muscle cells
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20
Q

What is the function of ANP and how does it achieve this?

A
  • Increased excretion of Na and water to reduce blood volume*
  • Inhibits ENaC to inhibit reabsorption
  • Supress production of renin, aldosterone and ADH
  • Increased GFR due to vasodilation
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21
Q

Where are stretch receptors (respiratory) located, where do the afferent fibres travel and what is the response?

A

Location: smooth muscle of bronchial walls

Afferent pathway: vagus nerve

Physiological response: short, shallow breaths and delay of the next inhalation cycle

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22
Q

What is the Hering-Breuer reflex (respiratory)?

A

Excessive lung inflation inhibits inspiratory muscle activity to prevent over inflation

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23
Q

Where are the Juxtapulmonary (J) receptors located, where do the afferent fibres travel, what activates them and what is the response?

A

Location: bronchial and alveolar walls

Afferent pathway: vagus nerve

Activation: oedema, microembolism, inflammation, fluid

Physiological response:
- apnoea or rapid, shallow breathing
- bradycardia and hypotension
- laryngeal constriction
- sensation of dyspnoea

24
Q

Which cells in the stomach is pepsinogen released from and what is its role?

A

Chief cells

Break down proteins in food into polypeptides

25
Q

What cells make up the gastric mucosa and what is released from each?

A

Parietal cells: HCl + intrinsic factor

Chief cells: Pepsinogen

ECL cells: Histamine

G-cells: Gastrin

D-cells: Somatostatin

26
Q

Describe the osmolality of the fluid travelling through the Loop of Henla

A

Entering: isotonic with plasma

Tip of hairpin: Hypertonic (in equilibrium with hypertonic interstitial fluid)

Exiting: Hypotonic

27
Q

Describe the permeabilities of the different regions of the Loop of Henle

A

DESCENDING
- permeable to water (passive transport out)
- impermeable to NaCl and urea

THIN ASCENDING
- impermeable to water
- permeable to NaCl and urea (passive transport out)

THICK ASCENDING
- impermeable to water
- permeable to NaCl (active transport out)

28
Q

What is the role of the vasa recta? (renal)

A

Removes the water which has been reabsorbed from the Loop of Henle and collecting ducts to maintain the osmotic gradient

29
Q

Action potentials are transmitted from myocyte to myocyte via what?

A

Gap junction

30
Q

What effect does angiotensin II have on afferent or efferent arterioles and what is the result?

A

Constricts efferent arterioles = increased glomerular capillary hydrostatic pressure = increased GFR

31
Q

What percentage of Na reabsorption happens in the various renal tubules and what channels are involved?

A

PROXIMAL TUBULE
- 65%
- Na/H exchanger

LOOP OF HENLE
- 25%
- NKCC2

EARLY DISTAL TUBULE
- 5%
- NaCl symporter

LATE DISTAL TUBULE
- 2%
- eNAC

32
Q

On a cellular level, describe the receptors and structures involved in vasoconstriction

A
  • Vasoconstrictors bind to G-protein coupled receptors
  • Elevation in intracellular Ca via
    a) release from sarcoplasmic reticulum
    b) entry via L-type VGCC
  • Vascular smooth muscle contraction
33
Q

On a cellular level, describe the receptors and structures involved in vasodilation

A
  • Decreased intracellular Ca via sequestration by the sarcoplasmic reticulum
  • Ca removal from the cell via NaCa exchange

The above is regulated via increased cGMP and cAMP

34
Q

Give examples of vasonstrictors and vasodilators

A

VASOCONSTRICTORS
- Endothelin 1
- Thromboxane A2
- Noradrenaline
- Angiotensin II

VASODILATORS
- B agonists
- Calcium channel blockers
- Nitric oxide
- Prostacyclin

35
Q

Where in the stomach does food mix with gastric secretion?

A

Distal body and antrum

36
Q

Gastric emptying is increased and decreased by what factors?

A

INCREASED
- Distension of the pyloric antrum
- A fall on the pH of chyme in the stomach
- Parasympathetics

DECREASED
- CCK
- Secretin
- Distension in the duodenum
- Presence of fat in the duodenum

37
Q

What are the muscular layers of the stomach?

A

Inner circular
Inner oblique
Outer longitudinal

38
Q

Starting with the renal artery, describe its divisions

A

Renal artery - segmental artery - interlobar artery - arcuate artery, interlobular artery - afferent arterioles of the glomerulus

39
Q

Describe the myogenic mechanism of renal blood flow autoregulation

A

Increased intravascular pressure = stretch receptors activated = smooth muscle contraction = vasoconstriction and reduced flow

40
Q

Describe the tubuloglomerular mechanism of renal blood flow autoregulation

A

Increased tubular flow rate = increased tubular NaCl concentration detected by the macula densa = juxtaglomerular apparatus releases adenosine = afferent arteriole vasoconstriction = reduced GFR

41
Q

What is the role of renin and what stimulates its release?

A

Promotes angiotensin II production = efferent arteriole vasoconstriction = increased GFR

  • Reduced pressure in the afferent arteriole
  • Reduced tubular flow rate (hence reduced NaCl concentration detected at the macula densa)
  • Sympathetic stimulation of B1 receptors
  • Reduced angiotensin II levels
42
Q

Where is renin released from?

A

Juxtaglomerular apparatus

43
Q

Give examples of renal vasoconstrictors and vasodilators

A

VASOCONSTRICTION:
- Angiotensin II
- Endothelin
- Vasopressin
- Noradrenalin

VASODILATION:
- Prostaglandins
- Nitric oxide
- Bradykinin
- Dopamine (low dose only)

44
Q

What properties of creatinine clearance allow it to provide an accurate estimate of GFR?

A
  • Freely filtered
  • Not reabsorbed or secreted in the nephron
  • Not synthesised or metabolised by the kidney
45
Q

Where is glucagon produced?

A

alpha cells located within the islets of Langerhans in the endocrine tissue of the pancreas

46
Q

Glucagon secretion is stimulated by what?

A
  • low blood glucose
  • high amino acids
  • CCK
  • Catecholamines
  • Acetylcholine
47
Q

What is the mechanism of action of glucagon and what does this result in?

A

Acts on g-protein coupled receptors to increase production of cAMP
- reduced glycogenesis
- reduced fatty acid synthesis
- increased glycogenolysis
- increased gluconeogenesis
- increased lipolysis
- increased ketoacid production

48
Q

Define:
a) glycogenesis
b) glycogenolysis
c) gluconeogenesis

A

a) storage of excess glucose as glycogen
b) glycogen is broken down into glucose
c) occurs when glycogen storage is low… glucose is made from proteins and lipids

49
Q

What factors effect blood flow through a tube? Which factor has the largest effect?

A
  • Pressure differences across the end of the tube
  • Resistance to flow (in itself determined by length of the tube, radius of the tube and viscosity of the fluid)

Radius of the tube has the largest effect on flow

50
Q

What is the mechanism of action of insulin and what processes does this result in?

A

Acts on tyrosine kinase receptors to activate a pathway that results in GLUT-4 transporters being present on the cell membrane

  • Increased glycogenesis
  • Increased protein synthesis
  • Increased fat deposition
  • Increased K uptake in to cells
  • Decreased glycogenolysis
  • Decreased gluconeogenesis
  • Decreased protein degradation
  • Decreased lipolysis
  • Decreased ketoacid production
51
Q

Which hormones are produced by the kidney?

A
  • Renin
  • Erythropoietin
  • Activated vitamin D
  • Prostaglandins
52
Q

The secretion of HCl into the stomach is stimulated by what factors?

A

Vagal stimulation
- Acetylcholine acts on M3 receptors on parietal cells
- Gastrin-releasing-peptide acting on G-cells to release gastrin

Histamine
- Acts on H2 receptors on parietal cells

Gastrin
- Released from G-cells and acts on the CCKB receptor of parietal cells

53
Q

What stimulates the secretion of erythropoietin?

A

Hypoxia or anaemia = reduced O2 supply to kidney = EPO secretion

54
Q

Describe the cell makeup of erythroblasts vs reticulocytes vs erythrocytes

A

ERYTHROBLASTS
- large and nucleated

RETICULOCYTES
- slightly smaller
- no nucleus
- network of ribosomal RNA for synthesis of Hb

ERYTHROCYTES
- small, biconcave discs with no nucleus, ribosomes or mitochondria

55
Q

Describe the process of red cell degredation (what happens to the breakdown products globin, haem and iron)

A
  1. Phagocytosis by macrophages in the bone marrow, liver and spleen
  2. GLOBIN
    - this protein portion of Hb is metabolized in to amino acids which are reused for protein synthesis

HAEM
- Broken down in to bilverdin and transferred to the liver
- Then converted to bilirubin

IRON
- Bind to transferrin for transfer to the liver
- then transferred to the protein ferritin for storage in the liver

MRCEM Primary (6 decks)

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