CH EXCRETORY PRODUCTS AND ELIMINATION

CH EXCRETORY PRODUCTS AND ELIMINATION fill ups

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Animals accumulate ________, ________, ________, ________ and ions like ______, _______, _______, _______, _______, either by metabolic activities or by other means like excess ingestion. These substances have to be removed totally or partially. In this chapter, you will learn the mechanisms of ________ of these substances with special emphasis on common nitrogenous wastes. ________, ________, and ________ are the major forms of nitrogenous wastes excreted by animals. ________ is the most toxic form and requires a ________ amount of water for its elimination, whereas ________, being the least toxic, can be removed with a ________ loss of water.

The process of excreting ammonia is called ________. Many ________ fishes, aquatic ________, and ________ insects are ammonotelic in nature. ________, as it is readily soluble, is generally excreted by ________ across body surfaces or through ________ surfaces (in fish) as ________ ions. ________ do not play any significant role in its removal. ________ adaptation necessitated the production of ________ toxic nitrogenous wastes like ________ and ________ for conservation of ________. ________, many terrestrial ________, and ________ fishes mainly excrete ________ and are called ________ animals. ________ produced by metabolism is converted into ________ in the ________ of these animals and released into the ________, which is filtered and excreted out by the ________. Some amount of ________ may be retained in the ________ matrix of some of these animals to maintain a desired ________.

________, ________, ________, and ________ excrete nitrogenous wastes as ________ in the form of ________ or ________ with a minimum loss of ________ and are called ________ animals.

A survey of the animal kingdom presents a variety of ________ structures. In most invertebrates, these structures are ________ tubular forms, whereas vertebrates have complex tubular organs called ________. Some of these structures are mentioned here. ________ or flame cells are the excretory structures in ________ (Flatworms, e.g., ________), rotifers, some ________, and the cephalochordate ________.

________ are primarily concerned with ________ and ________ regulation, i.e., osmoregulation. ________ are the tubular excretory structures of ________ and other ________. ________ help to remove ________ wastes and maintain a ________ and ________ balance.

________ tubules are the excretory structures of most ________, including ________. These tubules help in the removal of ________ wastes and ________. ________ glands or green glands perform the excretory function in crustaceans like ________.

16.1 Human Excretory System

In humans, the excretory system consists of a pair of ________, one pair of ________, a ________, and a ________. Kidneys are ________ brown, ________-shaped structures situated between the levels of the ________ thoracic and ________ lumbar vertebrae, close to the ________ wall of the ________ cavity.

Each kidney of an adult human measures ________ cm in length, ________ cm in width, ________ cm in thickness, with an average weight of ________ g.

Towards the center of the inner concave surface of the kidney is a notch called the ________, through which the ________, blood vessels, and nerves enter. Inner to the hilum is a broad, ________-shaped space called the ________, with projections called ________.

The outer layer of the kidney is a ________ capsule. Inside the kidney, there are two zones: an outer ________ and an inner ________. The ________ is divided into a few conical masses (________), projecting into the ________ (singular: ________).

Medullary pyramids as renal columns are called ________ (Figure 16.2).

Each kidney has nearly ________ complex tubular structures called ________ (Figure 16.3), which are the functional units. Each nephron has ________ parts – the ________ and the ________.

________ is a tuft of capillaries formed by the ________, a fine branch of the ________. Blood from the glomerulus is carried away by an ________.

The renal tubule begins with a ________ walled cup-like structure called ________, which encloses the ________. The ________ along with ________ is called the ________ or ________ (Figure 16.4).

The tubule continues further to form a highly coiled network – ________.

A ________ shaped ________ is the next part of the tubule, which has a ________ and an ________ limb. The ________ limb continues as another highly coiled tubular region called ________ (________).

The ________ of many nephrons open into a straight tube called ________, many of which converge and open into the ________ through ________ in the calyces.

The ________, ________, and ________ of the nephron are situated in the ________ region of the kidney, whereas the ________ dips into the ________. In the majority of nephrons, the loop of Henle is too ________ and extends only very little into the ________. Such nephrons are called ________.

In some nephrons, the ________ is very ________ and runs deep into the ________. These nephrons are called ________.

The ________ emerging from the glomerulus forms a fine capillary network around the renal tubule called the ________ capillaries. A minute vessel of this network runs parallel to the ________ forming a ‘U’ shaped ________. ________ is absent or highly reduced in ________.

16.2 Urine Formation

Urine formation involves three main processes, namely ________, ________, and ________, that take place in different parts of the nephron.

The first step in urine formation is the ________ of blood, which is carried out by the ________ and is called ________. On an average, ________ mL of blood is filtered by the kidneys per ________, which constitutes roughly ________ of the blood pumped out by each ________ of the heart in a minute.

The ________ capillary blood pressure causes filtration of blood through ________ layers, i.e., the ________ of glomerular blood vessels, the ________ of ________, and a ________ between these two layers.

The ________ cells of Bowman’s capsule, called ________, are arranged in an ________ manner to leave some minute spaces called ________ or ________. Blood is filtered so finely through these membranes that almost all the constituents of the ________, except the ________, pass onto the lumen of the ________.

Therefore, it is considered as a process of ________.

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The amount of the filtrate formed by the kidneys per minute is called ________ (________). GFR in a healthy individual is approximately ________ mL/minute, i.e., ________ litres per day!

The kidneys have built-in mechanisms for the regulation of ________. One such efficient mechanism is carried out by ________ (________). JGA is a special sensitive region formed by cellular ________ in the ________ and the ________ at the location of their contact. A ________ in GFR can activate the ________ cells to release ________, which can stimulate the ________ back to normal.

A comparison of the volume of the filtrate formed per day (________ litres per day) with that of the urine released (________ litres), suggests that nearly ________% of the filtrate has to be reabsorbed by the ________. This process is called ________.

The ________ in different segments of the nephron perform this either by ________ or ________ mechanisms. For example, substances like ________, ________, and ________ in the filtrate are reabsorbed actively, whereas the ________ are absorbed by ________ transport. ________ of water also occurs passively in the initial segments of the nephron.

During urine formation, the tubular cells secrete substances like ________, ________, and ________ into the filtrate. ________ is also an important step in urine formation as it helps in the maintenance of ________ and ________ balance of body fluids.

16.3 Function of the Tubules

Proximal Convoluted Tubule (PCT)

PCT is lined by ________ epithelium, which increases the ________ for ________. Nearly all of the essential nutrients, and ________ to ________% of ________ and ________, are reabsorbed by this segment.

PCT also helps to maintain the ________ and ________ balance of the body fluids by selective ________ of ________ and ________ into the filtrate and by ________ of ________ from it.

Henle’s Loop

Reabsorption is ________ in its ________ limb. However, this region plays a significant role in the maintenance of ________ of ________.

The ________ limb of the loop of Henle is ________ to water but almost ________ to electrolytes. This concentrates the filtrate as it moves ________. The ________ limb is ________ to water but allows ________ of ________ actively or passively.

Therefore, as the concentrated filtrate passes ________, it gets ________ due to the passage of ________ to the ________.

Distal Convoluted Tubule (DCT)

________ of ________ and ________ takes place in this segment. DCT is also capable of ________ of ________ and selective ________ of ________, ________, and ________, to maintain the ________ and ________ balance in the blood.

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Collecting Duct

This ________ duct extends from the ________ of the kidney to the ________ parts of the ________.

Large amounts of ________ could be reabsorbed from this region to produce a ________ urine. This segment allows passage of small amounts of ________ into the ________ to keep up the ________.

It also plays a role in the maintenance of ________ and ________ balance of blood by the selective secretion of ________ and ________ ions.

Here is the fill-in-the-blanks version for this section:

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16.4 Mechanism of Concentration of the Filtrate

Mammals have the ability to produce a ________ urine. The ________ and ________ play a significant role in this.

The flow of filtrate in the two limbs of ________ is in ________ directions and thus forms a ________ current. The flow of blood through the two limbs of ________ is ________

Counter Current Mechanism

The proximity between the ________ and ________, as well as the ________ in them, helps in maintaining an increasing ________ towards the inner medullary interstitium, i.e., from ________ mOsmolL⁻¹ in the cortex to about ________ mOsmolL⁻¹ in the inner medulla.

This gradient is mainly caused by ________ and ________. ________ is transported by the ________ limb of Henle’s loop, which is exchanged with the ________ limb of ________.

________ is returned to the interstitium by the ________ portion of ________. Similarly, small amounts of ________ enter the ________ segment of the ________ limb of Henle’s loop, which is transported back to the ________ by the collecting tubule.

The above-described transport of substances facilitated by the special arrangement of ________ and ________ is called the ________.

This mechanism helps to maintain a ________ gradient.

Presence of such ________ helps in an easy passage of water from the ________, thereby concentrating the filtrate (urine). Human kidneys can produce urine nearly ________ times more concentrated than the ________ formed.

16.5 Regulation of Kidney Function

The functioning of the kidneys is efficiently monitored and regulated by ________ mechanisms involving the ________, ________, and to a certain extent, the ________.

________ in the body are activated by changes in ________. An excessive loss of fluid from the body can activate these receptors, which stimulate the ________ to release ________ (ADH) or ________ from the neurohypophysis. ADH facilitates ________ of water and prevents ________. A(n) ________ in ADH release is generally known as ________.

Blood volume/osmotic changes can also affect kidney function by altering ________. An increase in blood pressure can ________ the GFR, whereas a decrease in blood pressure can ________ it.

The ________ plays a complex regulatory role. A fall in ________ can cause the JG cells to release ________, which converts ________ into ________. ________ is further converted into ________, which is a powerful vasoconstrictor.

Angiotensin II increases the ________, which leads to an increase in ________. It also activates the adrenal cortex to release ________, which causes reabsorption of ________ and water from the ________ tubules. This leads to an increase in ________.

This mechanism is called the ________. An increase in blood flow to the atria of the heart can cause the release of ________, which causes ________ and thereby decreases the blood pressure.

Therefore, as a check on the renin-angiotensin mechanism, ________ acts as a counter mechanism.

16.6 Micturition

Urine formed by the nephrons is ultimately carried to the ________, where it is stored until a voluntary signal is given by the ________. The process of expelling urine is called ________.

As the urinary bladder fills, it sends signals to the ________, which in response relaxes the ________ and allows urine to pass through the ________.

16.6 Micturition

To initiate the contraction of ________ muscles of the bladder and simultaneous relaxation of the ________ causing the release of urine. The process of release of urine is called ________, and the neural mechanisms causing it is called the ________ reflex.

An adult human excretes, on average, ________ litres of urine per day. The urine formed is a ________ coloured watery fluid that is slightly acidic (________) and has a characteristic odour. On average, ________ gm of urea is excreted per day.

Various conditions can affect the characteristics of urine. Analysis of urine helps in clinical diagnosis of many metabolic disorders as well as ________ of the kidney. For example, the presence of ________ (Glycosuria) and ________ (Ketonuria) in urine are indicative of ________.

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16.7 Role of Other Organs in Excretion

Other than the kidneys, ________, ________, ________, and ________ also help in the elimination of excretory wastes.

Our lungs remove large amounts of ________ (approximately ________ mL/minute) and also significant quantities of ________ every day.

The ________, the largest gland in our body, secretes ________ containing substances like ________, ________, ________, ________, and ________. Most of these substances ultimately pass out along with ________ wastes.

The ________ and ________ glands in the skin can eliminate certain substances through their secretions. Sweat produced by the sweat glands is a watery fluid containing ________, small amounts of ________, ________, and ________. Though the primary function of sweat is to facilitate a ________ effect on the body surface, it also helps in the removal of ________.

________ glands eliminate certain substances like ________, ________, and ________ through ________. This secretion provides a protective ________ covering for the skin. Do you know that small amounts of ________ wastes could be eliminated through ________ too?

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16.8 Disorders of the Excretory System

Malfunctioning of kidneys can lead to an accumulation of ________ in the blood, a condition called ________, which is highly harmful and may lead to ________. In such patients, ________ can be removed by a process called ________.

During the process of ________, the blood drained from a convenient artery is pumped into a ________ unit called ________. Blood drained from a convenient artery is pumped into a ________ unit after adding an ________ like ________.

The unit contains a coiled ________ tube surrounded by a fluid (________ fluid) having the same 

The composition is the same as that of plasma except for ________ wastes. The porous ________ membrane of the tube allows the passage of molecules based on ________ gradient. As nitrogenous wastes are absent in the ________ fluid, these substances freely move out, thereby clearing the ________. The cleared blood is pumped back to the body through a ________ after adding ________ to it. This method is a boon for thousands of ________ patients all over the world.

Kidney transplantation is the ultimate method in the correction of acute ________ (________ failure). A functioning kidney is used in transplantation from a ________, preferably a ________, to minimize its chances of ________ by the immune system of the host. Modern clinical procedures have increased the ________ rate of such a complicated technique.

Renal calculi: Stone or insoluble mass of ________ (________, etc.) formed within the kidney.

Glomerulonephritis: Inflammation of ________ of the kidney.

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Summary

Many nitrogen-containing substances, ________, ________, ________, ________, etc., that accumulate in the body have to be eliminated. The nature of nitrogenous wastes formed and their excretion varies among ________, mainly depending on the habitat (________ of water). ________, ________, and ________ are the major nitrogenous wastes excreted.

________, ________, ________, ________, and the ________ are the common excretory organs in animals. They not only eliminate nitrogenous wastes but also help in the maintenance of ________ and ________ balance of body fluids.

In humans, the excretory system consists of ________ kidneys, a pair of ________, a ________, and a ________. Each kidney has over ________ tubular structures called ________. ________ is the functional unit of the kidney and has two portions—________ and ________.

________ is a tuft of capillaries formed from ________ arterioles, fine branches of the ________. The ________ starts with a double-walled ________ and is further differentiated into a ________, ________, and ________ (________). The ________ of many nephrons join to a ________, many of which ultimately open into the ________ through the ________.

The ________ encloses the ________ to form the ________ or renal ________.

Urine formation involves three main processes:

1. ________

2. ________

3. ________

________ is a non-selective process performed by the ________ using the ________ pressure. About ________ mL of blood is filtered by the ________ per minute to form ________ mL of filtrate in the ________ per

Minute (________). ________, a specialized portion of the nephrons, plays a significant role in the regulation of ________. Nearly ________ percent reabsorption of the filtrate takes place through different parts of the nephrons. ________ is the major site of reabsorption and selective secretion. ________ primarily helps to maintain ________ (________ mOsmolL⁻¹ - ________ mOsmolL⁻¹) within the kidney interstitium. ________ and ________ allow extensive reabsorption of ________ and certain ________, which help in osmoregulation: ________, ________, and ________ could be secreted into the filtrate by the tubules to maintain the ________ and ________ of body fluids.

A ________ operates between the two limbs of the loop of ________ and those of ________ (capillary parallel to Henle’s loop). The filtrate gets ________ as it moves down the ________ limb but is ________ by the ________ limb. ________ and ________ are retained in the ________ by this arrangement. ________ and ________ concentrate the filtrate about ________ times, i.e., from ________ mOsmolL⁻¹ to ________ mOsmolL⁻¹, an excellent mechanism of ________.

Urine is stored in the ________ till a voluntary signal from ________ carries out its release through ________, i.e., ________. ________, ________, ________, and ________ also assist in excretion.

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