Q: Explain the physiology of urine formation. (8 Marks)
A: Urine is an aqueous solution containing water (96%), urea (2%) and
other dissolved substances (2%). The process of urine formation
involves glomerular filtration, selective reabsorption and tubular
secretion.
1. Glomerular filtration: Blood containing nitrogenous wastes flows
into the glomerulus through afferent arteriole with a pressure of 60
mm Hg. It is opposed by Bowman's capsular pressure of 18 mm Hg and
glomerular blood colloidal osmotic pressure of 32 mm Hg (18 + 32 = 50
mm Hg). The net filtration pressure is 10 mm Hg in the glomerular
capillaries.
It causes the filtration of blood through filtration membrane. The
process of pressure filtration through glomerular capillaries in
Bowman's capsule is known as glomerular filtration. The resultant
filtrate is called primary urine or glomerular filtrate.
It is hypotonic to cortical fluid. Glomerular filtrate contains water,
amino acids, glucose, salts of Na, K, Ca, Mg etc. Urea, Creatinine,
toxins etc. Glomerular filtrate passes through the renal tubule for
selective reabsorption and tubular secretion.
2. Selective reabsorption: The cells of renal tubule absorb the
essential substances from the glomerular filtrate by active transport,
passive transport etc. The process of absorption is unregulated in
proximal convoluted tubule (PCT) and loop of Henle (LOH) and is
regulated in distal convoluted tubule (DCT).
a. In PCT: The cuboidal cells with brush boarders in PCT absorb about
70 - 80% electrolytes and water along with all nutrients (glucose,
amino acids etc). Water is absorbed by Osmosis (Obligatory water
absorption). Na+ ions, glucose, amino acids and other essential
substances are absorbed by active transport. To maintain pH and ionic
balance of body fluids, cells of PCT secrete H+ and ammonia into the
glomerular filtrate. At the end of PCT, glomerular filtrate is
isotonic to cortical fluid.
b. In LOH:
i. in descending limb: In this part, about 15% of water is absorbed by
osmosis. Little amount of urea diffuses into descending limb and thus
concentration of renal fluid increases and isotonic to medullary
fluid.
ii. In ascending limb: This part is impermeable to water. Na+, Cl -,
Mg++, Ca++, K+, HCO3 - etc. are absorbed and H+ are secreted in this
part. Hence, glomerular filtrate is progressively diluted and at the
end of ascending limb, it is isotonic to medullary fluid.
c. In DCT: In this part, water is absorbed under the influence of
vasopressin (anti diuretic hormone - ADH) of pituitary gland
(Facultative water absorption). Under the influence of aldosterone
(adrenal hormone), Na+ ions are reabsorbed. Moreover, K+ and HCO3-
ions are absorbed and H+ and K+ ions are secreted. As a result,
glomerular filtrate becomes iosotic to cortical fluid.
d. In collecting duct: Little quantity of water is absorbed in this
part under the regulation of ADH. In addition, Na+ ions are absorbed
and H+ ions are secreted. As a result, at the end of collecting duct,
the glomerular filtrate is hypertonic to blood and is called urine.
3. Tubular secretion (Augmentation): During urine formation, cells of
renal tubule secrete H+ ions, K+ ions, ammonia, hippuric acid etc.
into the tubule. This process is called tubular secretion.
SSC English Grammar - Tenses Examples and Exercises for AP and Telangana Students
The TENSE of a VERB shows the TIME OF ITS ACTION and its degree of
completeness. There are three main tenses. Present, Past and Future.
Each of them has four forms.
Simple Present Tense Examples:
1. The sun rises in the East. (Truth)
2. We never go late to school. (Habit)
3. The circus show starts at night. (Announcement)
4. A stitch in time saves nine. (Proverb)
Present Continuous Tense Examples:
1. Look, the snake is going into the hole.
2. Don't disturb me, I am doing my homework.
Question: What are you doing?
Positive: I am watching TV.
Negative: I am not doing homework.
Present Perfect Tense Examples:
1. I have cut my finger (and it is bleeding now.)
2. We have lived in Utnoor for twenty years. (We are still living there.)
It is used for an action that is completed in the immediate past.
Eg: The newspaper has just come.
It is used for an action with no definite time.
Eg: I have seen this film.
Simple Past Tense Examples:
1. Columbus discovered America in 1498.
2. The plane to Mumbai took off a minute ago.
3. The old man died yesterday.
4. Abraham Lincoln abolished slavery centuries ago.
Past Continuous Tense Examples:
1. I was having a bath when the phone rang.
2. When we reached the bus stand, the bus was moving.
Past Perfect Tense Examples:
Fill in the blanks with either past simple or past perfect forms of
the verbs given in brackets.
1. By the time the doctor ........ the patient ...... (arrive/ die)
2. I ...... that I ..... to bring my keys. (find/ forget)
3. The teacher ........ our notebooks after he/ she ..... them.
(return/ correct)
Answers:
1. arrived/ had died
2. found/ had forgotten
3. returned/ had corrected
Past Perfect Continuous Examples:
Eg: 1. The phone had been ringing for five minutes but no one attended to it.
2. They had been living in Australia for two years before the World War began.
3. At that time he had been writing a novel for three months.
completeness. There are three main tenses. Present, Past and Future.
Each of them has four forms.
Simple Present Tense Examples:
1. The sun rises in the East. (Truth)
2. We never go late to school. (Habit)
3. The circus show starts at night. (Announcement)
4. A stitch in time saves nine. (Proverb)
Present Continuous Tense Examples:
1. Look, the snake is going into the hole.
2. Don't disturb me, I am doing my homework.
Question: What are you doing?
Positive: I am watching TV.
Negative: I am not doing homework.
Present Perfect Tense Examples:
1. I have cut my finger (and it is bleeding now.)
2. We have lived in Utnoor for twenty years. (We are still living there.)
It is used for an action that is completed in the immediate past.
Eg: The newspaper has just come.
It is used for an action with no definite time.
Eg: I have seen this film.
Simple Past Tense Examples:
1. Columbus discovered America in 1498.
2. The plane to Mumbai took off a minute ago.
3. The old man died yesterday.
4. Abraham Lincoln abolished slavery centuries ago.
Past Continuous Tense Examples:
1. I was having a bath when the phone rang.
2. When we reached the bus stand, the bus was moving.
Past Perfect Tense Examples:
Fill in the blanks with either past simple or past perfect forms of
the verbs given in brackets.
1. By the time the doctor ........ the patient ...... (arrive/ die)
2. I ...... that I ..... to bring my keys. (find/ forget)
3. The teacher ........ our notebooks after he/ she ..... them.
(return/ correct)
Answers:
1. arrived/ had died
2. found/ had forgotten
3. returned/ had corrected
Past Perfect Continuous Examples:
Eg: 1. The phone had been ringing for five minutes but no one attended to it.
2. They had been living in Australia for two years before the World War began.
3. At that time he had been writing a novel for three months.
10th Class English Grammar Exercises - Tenses in New Syllabus
Exercise1: Fill in the blanks with either simple present or present
continuous forms of the verbs given in brackets.
1. What ........ there? I ....... a large crowd. (happen/ see)
2. She ............ to be sick. (seem)
3. Shruthi always ......... late. But today she .......... early. (come)
Answers:
1) is happening, see 2) seems 3) comes, is coming.
Exercise 2: Fill in the blanks with the correct form of the Present
Perfect Continuous Tense of the verbs given in brackets.
1. Harshini and Sneha ........ for a long time. (quarrel)
2. Shruthi .... her homework since morning. (do)
3. We .............. in the same house since my childhood. (live)
4. My father ..... the newspaper for ten minutes. (read)
Answers:
1. have been quarrelling 2. has been doing 3. have been living 4. has
been reading.
Exercise 3: Fill in the blanks with the past simple or past continuous
forms of the verbs given in brackets.
1. Everyone ..... when the thief ...... the house. (sleep/ enter)
2. When power ..... Padmasri .... homework. (go off/ do)
3. Manasa .... tv when her aunt ..... . (watch/ arrive)
4. The firebrigade ...... when the huts ..... . (come/ burn)
Answers:
1. was sleeping/ entered
2. went off/ was doing
3. was watching/ arrived.
4. came/ were burning.
continuous forms of the verbs given in brackets.
1. What ........ there? I ....... a large crowd. (happen/ see)
2. She ............ to be sick. (seem)
3. Shruthi always ......... late. But today she .......... early. (come)
Answers:
1) is happening, see 2) seems 3) comes, is coming.
Exercise 2: Fill in the blanks with the correct form of the Present
Perfect Continuous Tense of the verbs given in brackets.
1. Harshini and Sneha ........ for a long time. (quarrel)
2. Shruthi .... her homework since morning. (do)
3. We .............. in the same house since my childhood. (live)
4. My father ..... the newspaper for ten minutes. (read)
Answers:
1. have been quarrelling 2. has been doing 3. have been living 4. has
been reading.
Exercise 3: Fill in the blanks with the past simple or past continuous
forms of the verbs given in brackets.
1. Everyone ..... when the thief ...... the house. (sleep/ enter)
2. When power ..... Padmasri .... homework. (go off/ do)
3. Manasa .... tv when her aunt ..... . (watch/ arrive)
4. The firebrigade ...... when the huts ..... . (come/ burn)
Answers:
1. was sleeping/ entered
2. went off/ was doing
3. was watching/ arrived.
4. came/ were burning.
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