NMDCAT (Parallel prep)
Biology
Homeostasis
Definition: The protection of internal environment from the harms of fluctuations in external
environment is called homeostasis
Mechanism of homeostasis
Variables: Internal factors influenced by external environment e.g. body temperature, water
concentration, solute composition etc.
Set point: Ideal or normal value of variable, already stored in memory or control center e.g. set
point for body temperature is 37℃
Examples
Osmoregulation: Maintenance of osmotic conditions (water & solute concentration) in the body.
Excretion: Mechanism which eliminates nitrogenous waste is called excretion
Thermoregulation: Maintenance of internal temperature with in a tolerable range.
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Components of control system
Sensors: Detect changes in variables
Control center: Interpret the information coming from sensor
Effectors: Show response
Components
Physical system
Living system
Sensors
Thermometer
Receptors
Control center
Thermostat
Hypothalamus
Effectors
Heating coil
Muscle or Gland
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Components of control system
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Feedback mechanism
Definition: Detection of change and signaling for effector’s response to the control center
OR
A cycle of events in which information about change is fed back into the system so that regulator
control system
Types: Two types of feedback mechanism
Positive feedback mechanism
Negative feedback mechanism
Amlify the change detected by receptor
Reverse the change detected by receptor
Destabilizing effects
Stabilizing effects
Does not help in homeostasis
Help in homeostasis
Less common in naturally occurring
systems
More common in naturally occurring
systems
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Negative feedback mechanism
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Positive feedback mechanism
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Multiple choice questions
Which one is true in relevance to cold weather?
•
Less urine is excreted
•
Excess salts are excreted in urine
•
Sweat secretions are reduced
•
Excess sugars are secreted in urine
Which is not an example of homeostasis?
• Oxygen content in the bloodstream is low, so the heart pumps faster and speed/depth of breathing increases
• Insulin is released by the pancreas to encourage cells to retain their glucose instead of releasing it into the blood stream
• Mitochondria create ATP through proton pumps in order to power the cellular processes
• Warm blooded (endothermic) animals sweat to release heat, or shiver to increase metabolic activity and increase body temperature
When the body needs to conserve water, antidiuretic hormone is secreted and the kidneys produce concentrated urine. This is an example of __________.
• vasoconstriction
• osmosis
• negative feedback
• reabsorption
• catabolism
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Multiple choice questions
Detection of change and signalling for effector’s inverse response to the control center is called
• Feedback mechanism
• Negative feedback mechanism
• Positive feedback mechanism
• All of the above
It is not true about positive feedback mechanism
• Has destabilizing effect
• Amplify the change detected by sensors
• Not involved to maintain homeostasis
• More common in naturally occuring systems
Oxytocin is produced by ----------- and secreted by ----------• Posterior lobe of pituitary & posterior lobe of pituitary
• Hypothalamus & posterior lobe of pituitary
• Hypothalamus & Hypothalamus
•
Hypothalamus & anterior lobe of pituitary
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Nitrogen containing excretory products
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Nitrogen containing excretory products
Features
Ammonia
Urea
Uric acid
Toxicity
Highly toxic
Less toxic (100,000 times)
Habitat
Excess supply of water
Moderate supply of water Restricted supply of water
H2O required to remove
1g N2 in the form of
500ml
50ml
1ml
Formula
NH3
CH₄N₂O
C5H4N4O3
Classification of animals
Ammonotelic
Ureotelic
Uricotelic
Examples
Most fishes, protozoans,
sponges, coelenterates.
Mammals, most
amphibians, sharks, some
bony fishes
Terrestrial invertebrates,
egg-laying vertebrates
Birds, insects, many
reptiles, land snails
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Least toxic
Nitrogen containing excretory products
• Mostly excess nitrogen is excreted by animals as ammonia, urea and uric acid.
• Lower quantities of nitrogen are excreted in the form of other compounds such as creatinine,
creatine or trimethylamine oxide
• Very small quantities as amino acids, purines and pyrimidines
• Metabolism of purines and pyrimidine bases produces significant amount of nitrogenous wastes
of hypoxanthine, xanthine, uric acid, urea, ammonia
Why ammonia is highly toxic?
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Excretory system of Human
Why left kidney is
superior than right
kidney in location?
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Human excretory system
• Weight of kidneys accounts for less than 1% of the total body weight
• Kidneys receive 20% of blood supplied with each cardiac beat
• The length of ureter is 25cm
• Internal urethral sphincter is present at the junction of urinary bladder and urethra control the urine in bladder
• External urethral sphincter are voluntary and control the process of micturition or urination
• Kidneys lie on either side of the vertebral column between the 12th thoracic and 3rd lumbar vertebrae
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Structure of kidney
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Multiple choice questions
Opening on the concave side of kidney where renal artery and nerves enter into kidney is termed as:
A. Renal sinus
B. Renal pelvis
C. Hilum or hilus
D. Renal cortex
Renal hilum extends into a large cavity called:
A. Renal pelvis
B. Renal sinus
C. Proximal part of ureter
D. Peritoneal cavity
It is not true about urinary bladder:
A. Located within abdominal cavity
B. Hollow distensible muscular organ
C. Serves as urine reservoir
D. Receive urine from ureters
Left kidney is superior in location than right kidney why?
A) Large liver above the right kidney
B) Because adrenal gland is present above the right kidney
C) Large liver above the left kidney
D) Because left kidney is present in thoracic cavity
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Multiple choice questions
Which of the following structure control the process of micturition?
A) Internal urethral sphincter
C) Ureteral orifices
B) External urethral sphincter
D) Urethra
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