(a) Elaborate on the hormonal regulation of blood glucose level. Explain in brief the signs and symptoms of hypoglycemia. 20…

(a) Hormonal regulation of blood glucose and hypoglycaemia

Fasting blood glucose is held at about 70–100 mg/dL by hormones that lower it (insulin) and hormones that raise it (counter-regulatory).

Insulin, from pancreatic β cells, is released when glucose rises after a meal. It increases glucose uptake in muscle and fat through GLUT4, and stimulates glycogenesis, glycolysis, lipogenesis and protein synthesis, while inhibiting glycogenolysis, gluconeogenesis, lipolysis and ketogenesis. It is the only hormone that lowers blood glucose.

Glucagon, from α cells, is released when glucose falls. It acts on the liver to stimulate glycogenolysis and gluconeogenesis, and to raise ketogenesis. Adrenaline acts rapidly in stress, increasing hepatic glycogenolysis, muscle glycogenolysis (lactate for gluconeogenesis) and lipolysis, and inhibiting insulin. Cortisol and growth hormone act more slowly: cortisol promotes gluconeogenesis and protein breakdown, and both reduce peripheral glucose use. Thyroid hormones, somatostatin and GLP-1 also modulate the pattern, GLP-1 increasing insulin release after meals.

Hypoglycaemia (plasma glucose below about 70 mg/dL, with symptoms in a diabetic and usually below 55 mg/dL in a non-diabetic person) is confirmed by Whipple's triad. Autonomic (neurogenic) symptoms are sweating, tremor, palpitations, anxiety, hunger and pallor. Neuroglycopenic symptoms are headache, confusion, blurred vision, slurred speech, behavioural change, seizures and coma.

(b) Vitamin C

Sources: citrus fruits, amla (Indian gooseberry), guava, papaya, tomato, capsicum, cabbage and green leafy vegetables. RDA (ICMR-NIN 2020): 80 mg/day for adult men and 65 mg/day for adult women.

Biochemical significance: as a cofactor for prolyl and lysyl hydroxylases it is essential for collagen synthesis and cross-linking; it supports carnitine synthesis and dopamine β-hydroxylase (noradrenaline synthesis); it is a water-soluble antioxidant that regenerates vitamin E; it reduces Fe³⁺ to Fe²⁺ and so improves non-haem iron absorption; and it helps in tyrosine metabolism, bile acid and steroid synthesis, and wound healing.

Deficiency (scurvy): early fatigue, irritability and weakness; then bleeding, swollen spongy gums and loose teeth, petechiae, perifollicular haemorrhages, corkscrew hairs, easy bruising, poor wound healing, painful joints with haemarthrosis and, in infants, subperiosteal haemorrhage and pseudoparalysis (Barlow disease). Anaemia is common. It responds to oral vitamin C.

(c)(i) Ulnar nerve

It arises from the medial cord of the brachial plexus (C8, T1; often C7). It runs down the medial side of the arm, pierces the medial intermuscular septum at mid-arm, passes behind the medial epicondyle, enters the forearm between the two heads of flexor carpi ulnaris, runs down with the ulnar artery, and enters the hand through Guyon's canal, dividing into superficial and deep branches.

Branches: in the forearm, muscular branches to flexor carpi ulnaris and the medial half of flexor digitorum profundus, the palmar cutaneous branch and the dorsal cutaneous branch. In the hand, the superficial branch supplies palmaris brevis and the skin of the medial 1½ fingers; the deep branch supplies the hypothenar muscles, the medial two lumbricals, all interossei, adductor pollicis and the deep head of flexor pollicis brevis. Damage causes a claw hand and loss of finger adduction and abduction.

(c)(ii) Portal vein and portacaval anastomoses

Formation: the portal vein, about 8 cm long, forms behind the neck of the pancreas, at the level of L1–L2, by the union of the superior mesenteric vein and the splenic vein. It ascends behind the first part of the duodenum, then in the free edge of the lesser omentum to the porta hepatis.

Tributaries: the splenic vein (with the inferior mesenteric vein, which usually joins it), the superior mesenteric vein, the left and right gastric veins, the cystic vein and the paraumbilical veins.

Portacaval anastomoses: (1) lower oesophagus, left gastric veins with oesophageal tributaries of the azygos system; (2) anal canal, superior rectal with middle and inferior rectal veins; (3) umbilicus, paraumbilical veins with superficial epigastric veins; (4) retroperitoneal, colic veins with renal and lumbar veins, and the bare area of the liver with phrenic veins. In portal hypertension, these dilate as oesophageal varices, haemorrhoids and caput medusae.