In animals, the main excretory products are, Ammonia- protozoans, crustaceans, platyhelminths, cnidarians, poriferans, echinoderms, fishes, larvae/tadpoles of amphibians are ammonotelic. Urea -cartilaginous fish, few bony fishes, adult amphibians and mammals including humans are uricotelic, Uric acid-terrestrial arthropods (including insects), lizards, snakes, and birds are uricotelic.

The heart is a pumping organ. It helps in circulation of deoxygenated blood all through the body. These helps in the oxygenation of blood. It is mainly located in the thoracic region. The waste materials present in the blood is filtered by the kidney.

The Urinary System, also known as the renal system or Urinary tract, consists of the kidneys, ureters, bladder, and the urethra .

True,

True,

Blood containing carbon dioxide flows from veins throughout the body to the heart, and then the heart pumps it to the lungs. Small air sacs (alveoli) in the lungs remove the carbon dioxide from the blood and release it into the lungs where it is exhaled. 

Urine is made in kidney from the kidney the ureter transports urine into the urinary bladder. The urinary bladder is a muscular sac. When it is empty, it is about the size and shape of a pear. The bladder stores urine, allowing urination to be infrequent and can be controlled. Urge for urination starts as bladder comes to have urine 400-450 ml. In response, the stretch receptors on the walls of the bladder send signals to the CNS. The CNS passes on motor messages to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.

The process of filtering the blood by the artificial kidney is known as dialysis. It is a method of removing excess water, nitrogenous wastes (urea), toxins from the blood in the patient who is rapidly developing loss of kidney function. It is also called renal replacement therapy. Hence dialysis is used as artificial kidney in kidney failure patients.

The kidneys are a pair of organs found along the posterior muscular wall of the abdominal cavity. They are attached to the dorsal body wall at the level of 12th thoracic to the 3rd lumbar vertebra in the abdominal cavity. Thus option B is the correct answer. 

• The process of expelling waste from the organism is called excretion. Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by the animals. Ammonia is the most toxic form and requires a large amount of water for its elimination, whereas uric acid, being the least toxic, can be removed with a minimum loss of water.
  
• The human excretory system consists of a pair of kidneys, ureter, urinary bladder and urethra.
  
• So, the correct answer is 'Excretion'.
  

One of the major organs of the excretory system are the kidneys. It's other major organ's are the urethra, sweat glands, lungs, and rectum. Gills in fish are part of the excretory system. The kidneys are very complex organs that play very important roles such as liquid waste is produced by the kidneys and stored in the muscular bladder. As blood flows through the capillaries, substances move from the blood through the capillary walls into the tubes. The urethra is a tube which connects the urinary bladder to the outside of the body. The urethra functions to both male and female bodies. It also functions as a passage for semen. There are two different types of sweat glands, the apocrine sweat glands, and the merocrine sweat glands. Both sweat glands contain muscle cells. Humans have two lungs, the left lung being divided into two lobes and the right with three. Lungs are what make you breathe and they also absorb water vapors. The rectum is about eight inches long and serves basically as storage for poop. 

The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals, including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species. It is within the uterus that the fetus develops during gestation, usually developing completely in placental mammals such as humans and partially in marsupials such as kangaroos and opossums. Two uteri usually form initially in a female and usually male fetus, and in placental mammals, they may partially or completely fuse into a single uterus depending on the species. In many species with two uteri, only one is functional. Ureter, urethra, and urinary bladder are parts of the excretory system.

Nitrogenous waste products are generated during the breakdown of proteins by the cells as they catabolize amino acids to obtain energy. During the process of deamination, enzymes remove the amino group as ammonia which is highly toxic even in small quantities. In humans, this is combined with carbon dioxide to give urea and uric acid, which is thrown out by the function of the kidneys in the form of urine. 

Renal physiology was described by Ludwig. Renal physiology is the study of the physiology of the kidney.

The liver is a large, meaty organ that sits on the right side of the belly. Weighing about 3 pounds, the liver is reddish-brown in color and feels rubbery to the touch. The liver has two large sections, called as the right and the left lobes. The gallbladder sits under the liver, along with parts of the pancreas and intestines. The liver and these organs work together to digest, absorb, and process food. 

Kidney is the main excretory organ in man. It helps in filtration of blood and maintains osmoregulation. Accessory organs of excretion are liver, lungs and skin. Lungs helps in excretion of carbon dioxide. Skin helps in secretion of oil, water and salts by sweat and sebaceous gland. Liver helps in excretion of bile. It also helps in formation of urea which is a major excretory product. So, the correct answer is option"kidneys."

Urethra in females serves the sole purpose of excretion of urine. It extends from the base of urinary bladder to the urinary meatus hence having a length of 4 cm.

a) Pelvis is the lower region of abdomen which houses various organs. 

a) Nephrons are structures located in the kidney which help in filteration of blood to form urine. 

The composition of urine in humans is 95% water, 2.5 % urea and 2.5% other waste. As urea is the major excretory waste humans are considered ureotelic., On an average, 25-30 g of urea is excreted out per day.

Urine is formed in the kidney. From the kidneys, two tubes called ureter one from each kidney descend to the urinary bladder which conducts urine from the kidneys to the urinary bladder. Urinary bladder receives and stores urine. Later, on stimulus urine is excreted to outside through urethra.

Although kidney is the main organs of excretion, several other organs also excrete wastes. They include the liver, skin, and lungs.  Excretory system of a human consists of kidneys, ureters, urinary bladder, and urethra.

The excretory system in the mammals deals with the absorption on the basis of the permeability of the system , among all the options given the option other than the function of the excretory system is releasing nitrogenous wastes.

A substance present in blood is filtered through kidneys. Depending on the concentration they are divided as follows, High threshold substances(such as chlorides or glucose), Low threshold substances (such as phosphates or urea). No-threshold substances (such as creatinine sulfate). The primary threshold substance is Urea and uric acid.

The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. Urine enters the bladder via the ureters and exits via the urethra. 

The urinary bladder is lined with transitional epithelium. It does not produce mucus.

The lungs, kidneys, and skin are excretory organs. Excess carbon dioxide is removed from the body through the lungs. Excess urea, water, and salts are removed by the kidneys and leave the body as urine. Excess water and salts also leave the body through the skin through sweat.

The urinary bladder is made up of several detrusor muscles which mainly expands and contracts by the signals received by the autonomic nervous system. Parasympathetic nerves from the S2, S3 and S4 levels of spinal cord cause the upper part of the bladder to contract and bladder neck to relax, assisting in the process of micturition (urination). Sympathetic nerves from the $T _{11}$-$L _2$ levels of spinal cord do the opposite, causing the upper section of the bladder to relax and the bladder neck to contract, ensuring urine storage.

Iris is supplied by involuntary muscles which contract or relax in response to photo stimuli. Gland ducts have muscles in their walls and in the form of sphincters which are involuntary. Coats of blood vessels also have a muscle layer sandwiched between two other layers. Urethra has two sphincters of which one is involuntary and one is voluntary. Hence, urethra is not exclusively supplied with involuntary muscles.

a) Dartos muscle is a muscle present in the scrotal sac.