GENERAL HUMAN PHYSIOLOGY - SECTION A

SECTION A - I. Elaborate On

1. Hormones Involved in Regulation of Blood Sugar Level - Functions of Insulin - Signs and Symptoms of Diabetes Mellitus (10 marks)

Part A: Hormones Involved in Regulation of Blood Sugar Level

• Secreted by the Beta (B) cells of the islets of Langerhans in the pancreas
• Released in response to rising blood glucose (e.g., after a meal)
• The primary hormone that lowers blood glucose

• Secreted by the Alpha (A) cells of the islets of Langerhans
• Released when blood glucose falls
• Stimulates hepatic glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (synthesis of glucose from non-carbohydrate precursors like amino acids)
• Acts opposite to insulin - raises blood glucose

• Released from the adrenal medulla during stress ("fight-or-flight")
• Stimulates glycogenolysis in both liver and muscle
• Raises blood glucose rapidly
• Also called a "counter-regulatory" or anti-insulin hormone

• Released from the adrenal cortex
• Promotes gluconeogenesis in the liver
• Decreases glucose uptake by peripheral tissues
• A counter-regulatory hormone - raises blood glucose

• Secreted by the anterior pituitary
• Has anti-insulin effects - decreases glucose uptake and utilization
• Promotes lipolysis, sparing glucose
• Raises blood glucose

• Increase glucose absorption from the gut
• Stimulate glycogenolysis

The interplay: Insulin is the only hormone that lowers blood glucose. All others (glucagon, epinephrine, cortisol, GH) are counter-regulatory and raise blood glucose.

Part B: Functions of Insulin

• Increases glucose uptake by muscle, adipose tissue, and other peripheral tissues by recruiting GLUT-4 transporters to the cell membrane
• Stimulates glycogenesis (glycogen synthesis) in liver and muscle
• Inhibits glycogenolysis (breakdown of glycogen)
• Inhibits gluconeogenesis in the liver
• Net result: lowers blood glucose (hypoglycemic effect)

• Promotes lipogenesis (fat synthesis from glucose)
• Inhibits lipolysis (breakdown of stored fat)
• Inhibits ketogenesis (formation of ketone bodies)

• Increases amino acid uptake by cells
• Stimulates protein synthesis
• Inhibits protein catabolism

• Promotes K⁺ entry into cells (lowers plasma K⁺)
• Increases Na⁺ retention by kidneys

• Stimulates cell growth and DNA synthesis

Note: Insulin acts via tyrosine kinase receptors on cell surfaces. Binding triggers receptor-mediated endocytosis and a cascade of intracellular signals.

Part C: Signs and Symptoms of Diabetes Mellitus

• Hyperglycemia - fasting blood glucose >126 mg/dL (diagnostic)
• Glycosuria - glucose spills into urine when blood glucose exceeds renal threshold (~180 mg/dL)
• Weight loss - despite increased appetite; due to lipolysis and protein catabolism
• Fatigue and weakness - cellular energy deficiency
• Blurred vision - osmotic changes in the lens
• Recurrent infections - impaired immune function and poor wound healing
• Ketosis and diabetic ketoacidosis (DKA) - in Type 1: fat breakdown produces ketone bodies (acetoacetate, β-hydroxybutyrate, acetone)
• Metabolic acidosis - from accumulation of ketoacids
• Kussmaul breathing - deep, labored breathing to compensate for acidosis
• Sweet (fruity) breath - from exhaled acetone
• Neuropathy - tingling/numbness in extremities (peripheral neuropathy)
• Diabetic coma - in severe untreated cases

Type 1 DM: Autoimmune destruction of B cells; presents acutely in children; requires insulin
Type 2 DM: Insulin resistance + B cell dysfunction; typically in overweight adults; managed with lifestyle changes and oral hypoglycemics

SECTION B - II. Write Notes On

1. Draw a Normal Electrocardiogram and Write Briefly About the Different Waves (5 marks)

Normal ECG Diagram:

The Waves and Their Significance:

Key Points:

• A positive deflection is written when depolarization moves toward the active electrode
• A negative deflection is written when depolarization moves away from the active electrode
• The ECG is recorded from 12 leads: 3 standard bipolar limb leads (I, II, III), 3 augmented unipolar leads (aVR, aVL, aVF), and 6 chest (precordial) leads (V1-V6)
• The PR interval reflects AV nodal delay (~0.1 s), which is shortened by sympathetic stimulation and lengthened by vagal stimulation

2. Micturition Reflex (5 marks)

Anatomy of Control:

• Detrusor muscle - smooth muscle of the bladder wall; contracts during micturition
• Internal urethral sphincter - smooth muscle; under involuntary (autonomic) control
• External urethral sphincter - skeletal muscle; under voluntary (somatic) control via pudendal nerve

The Micturition Reflex - Step by Step:

1. Bladder filling - As urine accumulates, the bladder wall stretches. Intravesical pressure rises progressively.
2. Stretch receptor activation - Sensory stretch receptors in the bladder wall (especially the posterior urethra) are activated. Signals travel via the pelvic nerves to the sacral segments (S2-S4) of the spinal cord.
3. Reflex arc - Parasympathetic signals return via the pelvic nerves to the detrusor muscle, causing it to contract. This is the core micturition reflex.
4. Self-regenerative cycle - Initial detrusor contraction further stretches receptors, generating more sensory impulses, causing stronger contraction - a positive feedback loop - until the bladder reaches strong contraction.
5. Sphincter inhibition - When the micturition reflex becomes strong enough, a reflex passes via the pudendal nerve to inhibit the external sphincter, allowing urine to flow.
6. Reflex fatigue - After a few seconds to over a minute, the reflex fatigues; the bladder relaxes, and intravesical pressure returns to baseline.

Higher Center Control:

• Brain stem (pons) - Contains both strong facilitative and inhibitory micturition centers
• Cerebral cortex - Mainly inhibitory; allows voluntary postponement of urination
• Higher centers keep the reflex partially inhibited; only when socially convenient do cortical centers facilitate the sacral micturition center and simultaneously relax the external sphincter
• Voluntary urination: Cortical centers facilitate the sacral centers + inhibit the external sphincter simultaneously

Abnormalities:

• Spinal cord injury above sacral level - reflex micturition is preserved but voluntary control is lost ("uninhibited bladder")
• Spinal cord injury at sacral level - abolishes the reflex entirely (atonic bladder/urinary retention)
• Infants - micturition is purely reflex until cortical control develops

3. Muscles of Respiration (5 marks)

Diagram:

A. Muscles of Inspiration (Active):

• The most important respiratory muscle; dome-shaped musculotendinous sheet separating thorax from abdomen
• Innervated by the phrenic nerves (C3, C4, C5)
• On contraction: the dome descends, increasing the vertical diameter of the thorax
• Has two parts: costal (attached to lower ribs) and crural (attached to vertebral ligaments)
• Either the diaphragm alone or external intercostals alone can maintain adequate ventilation at rest
• Transection above C3 is fatal without mechanical ventilation; below C5 spares phrenic nerves and preserves breathing

• Run obliquely downward and forward from rib to rib
• On contraction: elevate the lower ribs, increasing the anteroposterior and transverse diameter of the thorax (pump-handle and bucket-handle movements)
• Innervated by intercostal nerves

B. Muscles of Expiration:

Note: Abdominal muscles aid expiration by pushing the diaphragm upward (increased intra-abdominal pressure) and pulling the rib cage downward and inward.

Glottis Control:

• Abductor muscles of the larynx contract early in inspiration, opening the glottis wide to allow free airflow
• Adductor muscles close the glottis reflexively during swallowing to prevent aspiration

• Ganong's Review of Medical Physiology, 26th Edition
• Guyton and Hall Textbook of Medical Physiology
• Basic Medical Biochemistry: A Clinical Approach, 6th Edition