Seconday 5 (MYE) - Essay (9)

9. (a) Diagram 17 shows the various structures involved in the regulation of temperature in the human body. A worker enters a cold room that stores frozen meat. Explain how the regulation of the worker’s body temperature occurs. [10 marks]

Diagram 17













· When a worker enters a cold room, the slight drop in body temperature is detected by the hypothalamus when blood is transported to the brain [1]
· This causes impulses to be sent to the various body parts to carry out a negative feedback mechanism to bring the body temperature back to normal level [1]
· In the skin, the erector muscles contract to raise the hair shafts, trapping an insulating layer of warm and still air to prevent heat loss [1]
· Sweating does not occur and body heat is conserved [1]
· Vasocontriction occurs when the smooth muscles around the afferent arterioles contract to decrease the amount of blood flowing through the skin, hence reducing heat loss through radiation [1]
· Shivering occurs to generate heat energy [1]
· The adrenal gland will be stimulated to secrete more adrenaline [1]
· This causes an increase in the rate of breathing and heartbeat [1]
· The rate of glycogen conversion in the liver will also increase [1]
· The thyroid gland will also be stimulated to secrete thyroxine [1]
· This increases the rate of metabolism [1]
· More glucose will be metabolized in the muscle tissues to produce heat energy to warm the body [1]


(b) The urinary system consists of the kidneys which play an essential role in controlling the composition and volume of the body fluids. The kidneys receive blood from the abdominal aorta via the renal artery and the renal veins return blood to the inferior vena cava.

*Concentration of substances in solution (g/dm3)


Glucose
Blood plasma entering glomerulus = 1.0
Glomerular filtrate = 1.0
Urine produced by kidneys = 0.0

Amino acid
Blood plasma entering glomerulus = 1.5
Glomerular filtrate = 1.5
Urine produced by kidneys = 0.0

Protein
Blood plasma entering glomerulus = 8.0
Glomerular filtrate = 0.0
Urine produced by kidneys = 0.0

Urea
Blood plasma entering glomerulus = 0.3
Glomerular filtrate = 0.3
Urine produced by kidneys = 20.0

Sodium ions
Blood plasma entering glomerulus = 3.2
Glomerular filtrate = 3.2
Urine produced by kidneys = 3.5

Table 1 shows the concentration of some substances in the blood plasma, glomerular filtrate and urine of an adult. Based on the table, describe how the process of urine formation occurs in an individual. [10 marks]

· When blood flows from the afferent arteriole to the narrower efferent arteriole, the high hydrostatic pressure forces [1] the blood plasma across the filtration membrane into the Bowman’s capsule via ultrafiltration [1]
· The content of the blood plasma such as glucose, amino acids, urea, sodium ions and other ions will be present in the glomerular filtrate [1] except for red blood cells and the large protein molecules [1]
· The filtrate will be passed through the proximal convoluted tubule [1] where reabsorption of useful molecules takes place [1]
· Amino acids and glucose are both actively reabsorbed [1] from the proximal convoluted tubule into the blood in the peritubular capillaries [1]
· As the filtrate is passing along the renal tubule, some sodium ions will be secreted from the blood into the distal convoluted tubule [1]
· A large quantity of urea will be secreted from the renal tubules to be removed in the urine [1]