Biology Flashcards

Question 1

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Central nervous system?

Answer

A

CNS includes the brain and the spinal cord and is the site of information processing and control.

Question 2

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Brain inside skull?

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A

The brain is enclosed within the skull, which provides frontal, lateral and dorsal protection. The skull consists of 22 bones, 14 of which form the facial bones and the remaining 8 form the cranial bones. Anatomically, the brain is contained within the cranium and is surrounded by the cerebrospinal fluid.

The Cerebrospinal Fluid (CSF) is a fluid that circulates within the skull and spinal cord, filling up hollow spaces on the surface of the brain.Every day, thespecialised ependymal cells produce around 500mL of cerebrospinal fluid.

The primary function of the CSF is to act as a buffer for the brain, cushioning mechanical shocks and dampening minor jolts. It also provides basic immunological protection to the brain.

Furthermore, CSF provides buoyancy for the brain. i.e., the brain is suspended in a layer of CSF, wherein, the weight of the brain is nearly negated. If the brain is not suspended in CSF, it would be impeded by its weight, consequently cutting off the blood supply in the lower half of the brain. It would lead to the death of neurons in the affected area.

<ul><li>The human brain is well protected by the skull. Inside the skull, the brain is covered by cranial meninges consisting of an outer layer called dura mater, a very thin middle layer called arachnoid and an inner layer (which is in contact with the brain tissue) called pia mater.</li></ul>

Question 3

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Three parts of brain?

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A

<ol><li>Forebrain</li><li>Mid brain</li><li>hindbrain</li></ol>

Question 4

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Forebrain?

Answer

A

It is the anterior part of the brain.

The forebrain consists of cerebrum, thalamus and Limbic system (hypothalamus).

Controls the reproductive functions, body temperature, emotions, hunger and sleep.

Question 5

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Mid brain?

Answer

A

Smallest and central part of the brain

The midbrain consists of:

<ul><li>Tectum</li><li>Tegmentum</li></ul>

The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passess through the midbrain.

Question 6

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Hindbrain?

Answer

A

The lower part of the brain

Thehindbrain is composed of:

<ul><li>Cerebellum</li><li>Medulla</li><li>Pons</li></ul>

Hindbrain functions: The three regions of the hindbrain coordinates all processes necessary for survival. These induce breathing, heartbeat, sleep, wakefulness and motor learning.

Question 7

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Cerebrum: structure?

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A

<ul><li>the largest part of the brain.</li><li>It consists of the cerebral cortex (layer of cells which covers the cerebral hemisphere) and other subcortical structures. The cerebral cortex is referred to as the grey matter due to its greyish appearance. The neuron cell bodies are concentrated here giving the colour.</li></ul>

<ul><li>Fibres of the tracts are covered with the myelin sheath, which constitute the inner part of cerebral hemisphere. They give an opaque white appearance to the layer and, hence, is called the white matter.</li></ul>

<ul><li>It is composed of two cerebral hemispheres that are joined together by heavy, dense bands of fibrecalled thecorpus callosum.</li><li>The cerebrum is further divided into four sections or lobes:<ul><li>Frontal lobe: It is associated with parts of speech, planning, reasoning, problem-solving and movements.</li><li>Parietal lobe: Help in movements, the perception of stimuli and orientation.</li><li>Occipital lobe: It is related to visual processing.</li><li>Temporal lobe: This region is related to perception and recognition of memory, auditory stimuli and speech.</li></ul></li><li>The exterior portion of the cerebrum is called the cortex or the cerebral mantle. The cortex is extremely convoluted, due to which, it has a large surface area.</li><li>The cerebrum also includes:<ul><li>Sensory areas: Toreceive the messages.</li><li>Association areas: These areas integrate the incoming sensory information. It also forms a connection between sensory and motor areas.</li><li>Motor areas: This area is responsible for the action of the voluntary muscles.</li></ul></li></ul>

Question 8

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The brain consists of two types of tissues?

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A

<ol><li>Grey matter mainly consists of various types of cells, which make up the bulk of the brain.</li><li>White matter is primarily composed of axons, which connect various grey matter areas of the brain with each other.</li></ol>

Question 9

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Cerebrum:functions?

Answer

A

The cerebrum is responsible for thinking, intelligence, consciousness and memory. It is also responsible for interpreting touch, hearing and vision.

Question 10

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Thalamus?

Answer

A

The thalamus is a small structure, located right above the brain stem responsible for relaying sensory information from the<a>sense organs</a>.

It is also responsible for transmitting motor information for movement and coordination.

Thalamus is found in thelimbic systemwithin the cerebrum. Thislimbic system is mainlyresponsible for the formation of new memories and storing past experiences.

Question 11

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Hypothalamus?

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A

located precisely below the thalamus. It is considered the primary region of the brain, as it is involved in the following functions:

<ol><li>Receives impulses</li><li>Regulates body temperature</li><li>Controls the mood and emotions</li><li>Controls the sense of taste and smell</li><li>Synthesises the body’s essential hormones</li><li>Coordinates the messages from the autonomous nervous system</li><li>Controls appetite, peristalsis, the rateof heartbeat, andblood pressure</li><li>Forms an axis with the pituitary gland which is the main link between the nervous and the endocrine systems</li></ol>

Question 12

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Tectum?

Answer

A

The tectumis a small portion of the brain, specifically thedorsalpart of themidbrain. It serves as a relay centre for the sensory information from the ears to the cerebrum. It also controls the reflex movements of the head, eye and neck muscles. It provides a passage for the different neurons moving in and out of the cerebrum.

Question 13

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Tegmentum?

Answer

A

Tegmentum is a region within the brainstem. It is a complex structure with various components, which is mainly involved in body movements, sleep, arousal, attention, and different necessary reflexes. It forms the platform for the midbrain and connects with thethalamus, cerebral cortex and the spinal cord.

Question 14

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Cerebellum?

Answer

A

the second largest part of the brain, located in the posterior portion of the medulla and pons.

The cerebellum and cerebrum are separated by cerebellar tentorium and transverse fissure.

Cortex is the outer surface of the cerebellum, and its parallel ridges are called the folia.

Apart from this, the cerebellum has the cerebellar peduncles, cerebellar nuclei, anterior and posterior lobes.

The cerebellum consists of two hemispheres, the outer grey cortex and the inner white medulla.

The main functions ofthe cerebellum include:

<ol><li>It senses equilibrium.</li><li>Transfers information.</li><li>Coordinates eye movement.</li><li>It enables precision control of the voluntary body movements.</li><li>Predicts the future position of the body during a particular movement.</li><li>Both anterior and posterior lobes are concerned with the skeletal movements.</li><li>The cerebellum is also essential for making fine adjustments to motor actions.</li><li>Coordinates and maintains body balance and posture during walking, running, riding, swimming.</li></ol>

Question 15

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Medulla Oblongata?

Answer

A

The medulla oblongata is a small structure present in the lowest region of the brain. It mainly controls the body’s autonomic functions such as heartbeat, breathing, and digestion. It plays a primary role in connecting the spinal cord, pons and the cerebral cortex. Also, it helps us in maintaining our posture and controlling our reflexes.

Question 16

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Pons?

Answer

A

The pons is the primary structure of the brain stem present between the midbrain and medulla oblongata. It serves as a relay signalsbetween the lower cerebellum, spinal cord, the midbrain, cerebrum and other higher parts of the brain. The main functions ofthe pons include:

<ol><li>Controlling sleep cycles.</li><li>Regulating the magnitude and frequency of the respiration.</li><li>Transfers information between the cerebellum and motor cortex.</li><li>Pons is also involved insensations, such as the sense of taste, hearing and balance.</li></ol>

Question 17

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Limbic system?

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A

<ul><li>The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc., form a complex structure called the limbic lobe or limbic system. Along with the hypothalamus, it is involved in the regulation of sexual behaviour, expression of emotional reactions (e.g., excitement, pleasure, rage and fear), and motivation.</li></ul>

Question 18

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Neuron structure?

Answer

A

composed of three major parts, namely, cell body, dendrites and axon

The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s granules

There are two types of axons, namely, myelinated and nonmyelinated. The myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier. Myelinated nerve fibres are found in spinal and cranial nerves. Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon, and is commonly found in autonomous and the somatic neural systems

Question 19

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endocrine glands?

Answer

A

<ol><li>Hypothalamus</li><li>Pituitary</li><li>Pineal</li><li>Thyroid and Parathyroid</li><li>Thymus</li><li>Pancreas</li><li>Adrenal</li><li>Testes and Ovary</li></ol>

Question 20

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Hypothalamus (endocrine gland)

Answer

A

<ul><li>These hormones regulate the synthesis and secretion of pituitary hormones. However, the hormones produced by hypothalamus are of two types, the releasing hormones (which stimulate secretion of pituitary hormones) and the inhibiting hormones (which inhibit secretions of pituitary hormones).</li><li>For example a hypothalamic hormone called Gonadotrophin releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins. On the other hand, somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary.</li><li>These hormones originating in the hypothalamic neurons, pass through axons and are released from their nerve endings. These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus.</li></ul>

Question 21

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Pituitary gland?

Answer

A

<ul><li>located in a bony cavity called sella tursica and is attached to hypothalamus by a stalk.</li><li>Consists of three parts<ul><li>Pars distallis also called anterior pituitary</li><li>Pars intermedia: in humans, the pars intermedia is almost merged with pars distalis.</li><li>Pars nervosa also called posterior pituitary</li><li>Pars distallis and Pars intermedia form adenohypophysis while pars nervosa is called neurohypophysis</li></ul></li><li>Pars distallis produces<ul><li>Growth Hormone (GH): Over-secretion of GH stimulates abnormal growth of the body leading to gigantism and low secretion of GH results in stunted growth resulting in pituitary dwarfism.</li><li>Prolactin: regulates the growth of the mammary glands and formation of milk in them</li><li>Thyroid stimulating Hormone (TSH): stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.</li><li>ACTH: stimulates the synthesis and secretion of steroid hormones from adrenal cortex</li><li>LH and FSH: stimulate gonadal activity and hence are called gonadotrophins. Spermatogenesis in males and ovulation in females</li></ul></li><li>Pars intermedia secretes only MSH: MSH acts on the melanocytes (melanin containing cells) and regulates pigmentation of the skin.</li><li>Pars nervosa: stores and releases two hormones called oxytocin and vasopressin, which are actually synthesised by the hypothalamus and are transported axonally to neurohypophysis.<ul><li>Oxytocin acts on the smooth muscles of our body and stimulates their contraction. In females, it stimulates a vigorous contraction of uterus at the time of child birth, and milk ejection from the mammary gland.</li><li>Vasopressin acts mainly at the kidney and stimulates resorption of water and electrolytes by the distal tubules and thereby reduces loss of water through urine (diuresis). Hence, it is also called as Anti-Diuretic Hormone (ADH).</li></ul></li></ul>

Question 22

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Pineal Gland

Answer

A

<ol><li>located on the dorsal side of forebrain.</li><li>secretes a hormone called melatonin</li><li>melatonin plays a role in<ol><li>diurnal rhythm</li><li>body temp</li><li>metabolism</li><li>pigmentation</li><li>menstrual cycle</li></ol></li></ol>

Question 23

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Thyroid Gland?

Answer

A

<ol><li>composed of two lobes which are located on either side of the trachea. Both the lobes are interconnected with a thin flap of connective tissue called isthmus.</li><li>Two hormones<ol><li>T3</li><li>T4 aka Thyroxine</li><li>also secretes a protein hormone called Thyrocalcitonin (TCT) which regulates the blood calcium levels.</li></ol></li></ol>

<ul><li>Iodine is essential for the normal rate of hormone synthesis in the thyroid. Deficiency of iodine in our diet results in hypothyroidism and enlargement of the thyroid gland, commonly called goitre.Hypothyroidism during pregnancy causes defective development and maturation of the growing baby leading to stunted growth (cretinism), mental retardation, low intelligence quotient, abnormal skin, deaf-mutism, etc. In adult women, hypothyroidism may cause menstrual cycle to become irregular.</li><li>Thyroid hormones play an important role in<ul><li>basal metabolic rate</li><li>RBC formation</li><li>contols metabolsim of carbohydrates, proteins, fats</li><li>maintenance of electrolyte and water balance</li></ul></li></ul>

Question 24

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Parathyroid gland

Answer

A

<ol><li>four parathyroid glands are present on the back side of the thyroid gland, one pair each in the two lobes of the thyroid gland.</li><li>secrete a peptide hormone called Parathyroid Hormone (PTH). The secretion of PTH is regulated by the circulating levels of calcium ions. Parathyroid hormone (PTH) increases the Ca2+ levels in the blood.</li><li>PTH is a Hypercalcemic Hormone, i.e., it increases the blood Ca2+ levels. PTH acts on bones and stimulates the process of bone resorption (dissolution/ demineralisation). Along with TCT, it plays a significant role in calcium balance in the body.</li></ol>

Question 25

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Thymus?

Answer

A

<ol><li>lobular structure located between lungs behind sternum</li><li>secretes the peptide hormones called Thymosins. that plays a major role in the development of the immune system</li></ol>

<ul><li>Thymosins play a major role in the differentiation of T-lymphocytes, which provide cell-mediated immunity.</li><li>In addition, thymosins also promote production of antibodies to provide humoral immunity.</li><li>Thymus is degenerated in old individuals resulting in a decreased production of thymosins. As a result, the immune responses of old persons become weak.</li></ul>

Question 26

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Adrenal Gland?

Answer

A

<ol><li>one pair of adrenal glands, one at the anterior part of each kidney. The gland is composed of two types of tissues. The centrally located tissue is called the adrenal medulla, and outside this lies the adrenal cortex.</li><li>Adrenal Medulla secretes two hormones, called catecholamines<ul><li>adrenaline (aka epinephrine)</li><li>noradrenaline</li></ul></li></ol>

<ul><li>Adrenaline and noradrenaline are rapidly secreted in response to stress of any kind and during emergency situations and are called emergency hormones or hormones of Fight or Flight. These hormones increase alertness, pupilary dilation, piloerection (raising of hairs), sweating etc.</li></ul>

<ul><li>Catecholamines also stimulate the breakdown of glycogen resulting in an increased concentration of glucose in blood. In addition, they also stimulate the breakdown of lipids and proteins.</li></ul>

3. The adrenal cortex secretes many hormones, commonly called as corticoids. The corticoids, which are involved in carbohydrate metabolism are called glucocorticoids. In our body, cortisol is the main glucocorticoid. Corticoids, which regulate the balance of water and electrolytes in our body are called mineralocorticoids. Aldosterone is the main mineralocorticoid in our body.

<ul><li>Cortisol is also involved in maintaining the cardio-vascular system as well as the kidney functions.</li><li>Glucocorticoids, particularly cortisol, produces anti-inflammatory reactions and suppresses the immune response.</li><li>Cortisol stimulates the RBC production.</li><li>Aldosterone acts mainly at the renal tubules and stimulates the reabsorption of Na+ and water and excretion of K+ and phosphate ions. Thus, aldosterone helps in the maintenance of electrolytes, body fluid volume, osmotic pressure and blood pressure.</li><li>Small amounts of androgenic steroids are also secreted by the adrenal cortex which play a role in the growth of axial hair, pubic hair and facial hair during puberty.</li></ul>

Question 27

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Pancreas?

Answer

A

<ul><li>Pancreas is a composite gland which acts as both exocrine and endocrine gland.<ul><li>The endocrine pancreas consists of ‘Islets of Langerhans’. There are about 1 to 2 million Islets of Langerhans in a normal human pancreas representing only 1 to 2 per cent of the pancreatic tissue.</li><li>The two main types of cells in the Islet of Langerhans are called a-cells and p-cells. The a-cells secrete a hormone called glucagon, while the p-cells secrete INSULIN.</li></ul></li><li>Glucagon is a peptide hormone, and plays an important role in maintaining the normal blood glucose levels. Glucagon acts mainly on the liver cells (hepatocytes) and stimulates glycogenolysis resulting in an increased blood sugar (hyperglycemia).</li><li>Insulin is a peptide hormone, which plays a major role in the regulation of glucose <a>homeostasis</a>. Insulin acts mainly on hepatocytes and adipocytes (cells of adipose tissue), and enhances cellular glucose uptake and utilisation. As a result, there is a rapid movement of glucose from blood to hepatocytes and adipocytes resulting in decreased blood glucose levels (hypoglycemia).</li><li>The glucose <a>homeostasis</a> in blood is thus maintained jointly by the two – insulin and glucagons.</li><li>Prolonged hyperglycemia leads to a complex disorder called diabetes mellitus which is associated with loss of glucose through urine and formation of harmful compounds known as ketone bodies. Diabetic patients are successfully treated with insulin therapy.</li></ul>

Question 28

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Testis?

Answer

A

<ol><li>Testis performs dual functions as a primary sex organ as well as an endocrine gland.</li><li>produces group of hormones called androgens mainly testosterone.</li></ol>

<ul><li>Androgens regulate the development, maturation and functions of the male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, urethra etc.</li><li>These hormones stimulate muscular growth, growth of facial and axillary hair, aggressiveness, low pitch of voice etc.</li><li>Androgens play a major stimulatory role in the process of spermatogenesis (formation of spermatozoa).</li><li>Androgens act on the central neural system and influence the male sexual behavior (libido).</li><li>These hormones produce anabolic (synthetic) effects on protein and carbohydrate metabolism.</li></ul>

Question 29

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Ovary?

Answer

A

<ol><li>produces two groups of steroid hormones called estrogen and progesterone. The estrogen is synthesized and secreted mainly by the growing ovarian follicles. After ovulation, the ruptured follicle is converted to a structure called corpus luteum, which secretes mainly progesterone.</li></ol>

<ul><li>Estrogens produce wide ranging actions such as stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, appearance of female secondary sex characters (e.g., high pitch of voice, etc.), mammary gland development. Estrogens also regulate female sexual behavior.</li><li>Progesterone supports pregnancy. Progesterone also acts on the mammary glands and stimulates the formation of alveoli (sac-like structures which store milk) and milk secretion.</li></ul>

Question 30

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Hormones of Heart, Kidney and GI Tract

Answer

A

<ul><li>hormones are also secreted by some tissues which are not endocrine glands.</li><li>For example, the atrial wall of our heart secretes a very important peptide hormone called Atrial Natriuretic Factor (ANF), which decreases blood pressure. When blood pressure is increased, ANF is secreted which causes dilation of the blood vessels. This reduces the blood pressure.</li><li>The juxtaglomerular cells of kidney produce a peptide hormone called erythropoietin which stimulates Erythropoiesis (formation of RBC).</li></ul>

<ul><li>Endocrine cells present in different parts of the gastro-intestinal tract secrete four major peptide hormones, namely Gastrin, Secretin, Cholecystokinin (CCK) and Gastric Inhibitory Peptide (GIP).<ul><li>Gastrin acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen.</li><li>Secretin acts on the exocrine pancreas and stimulates secretion of water and bicarbonate ions.</li><li>CCK acts on both pancreas and gall bladder and stimulates the secretion of pancreatic enzymes and bile juice, respectively.</li><li>GIP inhibits gastric secretion and motility.</li></ul></li></ul>

Question 31

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Buccal Cavity?

Answer

A

<ol><li>The process of taking food into the body is called ingestion.</li><li>Teeth<ol><li>Majority of mammals including human being forms two sets of teeth during their life</li><li>Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which in human is 2123/2123 [2-I,1-C,2-PM,3-M]</li></ol></li><li>Our mouth has the salivary glands which secrete saliva. The saliva breaks down the starch into sugars. The saliva secreted into the oral cavity contains electrolytes (Na+, K+, Cl”, HCOs) and enzymes, SALIVARY AMYLASE and LYSOZYME. The chemical process of digestion is initiated in the oral cavity by the hydrolytic action of the carbohydrate splitting enzyme, the salivary amylase. About 30 per cent of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide – maltose. Lysozyme present in saliva acts as an antibacterial agent that prevents infections.</li><li>The tongue is attached to the floor of the oral cavity by the frenulum (a fold of skin beneath the tongue). The upper surface of the tongue has small projections called papillae, some of which bear taste buds.</li></ol>

Question 32

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Oesophagus?

Answer

A

<ol><li>oral cavity leads into a short pharynx which serves as a common passage for food and air. The esophagus and the trachea (wind pipe) open into the pharynx</li></ol>

<ul><li>A cartilaginous flap called epiglottis prevents the entry of food into the glottis during swallowing. [Glottis == opening of the wind pipe].</li><li>Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition.</li><li>The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis. The gastro-oesophageal sphincter controls the passage of food into the stomach.</li></ul>

Question 33

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Stomach?

Answer

A

<ul><li>inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices.</li></ul>

<ol><li>The mucous protects the lining of the stomach. mucous is produced by epithelial cells in the outer layer</li><li>The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic. The layer inside the epithelial layer is called oxyntic layer, that produces hydro chloric acid</li><li>The digestive juices break down the proteins into simpler substances.</li></ol>

<ul><li>The stomach, located in the upper left portion of the abdominal cavity, has three major parts – a cardiac portion into which the oesophagus opens, a fundic region and a pyloric portion which opens into the first part of small intestine.</li><li>The stomach stores the food for 4-5 hours. The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the chyme.</li><li>gastric glands produce two enzymes- pepsin and renin. Both help in protein digestion. Renin helps in digesting Caseinogen, protein in milk.</li><li>The proenzyme [inactive precursor of an enzyme] pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme PEPSIN, the proteolytic (breakdown of proteins or peptides into amino acids) enzyme of the stomach.</li><li>Pepsin converts proteins into proteoses and peptones (peptides).</li><li>The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. HCl provides the acidic pH (pH 1.8) optimal for pepsins.</li><li>Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins.</li></ul>

Question 34

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Small intestine?

Answer

A

<ul><li>distinguishable into three regions, a ‘C’ shaped duodenum, a long coiled middle portion jejunum and a highly coiled ileum.<ul><li>The opening of the stomach into the duodenum is guarded by the pyloric sphincter. Ileum opens into the large intestine.</li></ul></li><li>The small intestine is highly coiled and is about 5 meters long. It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices.</li><li>these enzymes and secretions are received in the duodenum. The breakdown of biomacromolecules like proteins into dipeptides or amino acids or fats into fatty acids, occurs in the duodenum region of the small intestine. The simple substances thus formed are absorbed in the jejunum and ileum regions of the small intestine.</li><li>The secretions of the mucosa along with the bicarbonates from the pancreas protects the intestinal mucosa from acid as well as provide an alkaline medium (pH 7.8) for enzymatic activities.</li><li>The digested food passes into the blood vessels in the wall of the intestine. This process is called absorption.</li><li>The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi (singular villus). The villi increase the surface area for absorption of the digested food.<ul><li>Villi are supplied with a network of capillaries and a large lymph (a colourless fluid containing white blood cells) vessel called the lacteal.</li></ul></li><li>The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by the body. This is called assimilation.</li><li>The food that remains undigested and unabsorbed then enters into the large intestine.</li></ul>

Question 35

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Large intestine?

Answer

A

<ul><li>The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length. Its function is to absorb water and some salts from the undigested food material.</li><li>The remaining waste passes into the rectum and remains there as semi-solid faeces. The faecal matter is removed through the anus from time-to-time. This is called egestion.</li><li>It consists of caecum, colon and rectum. Caecum is a small blind sac which hosts some symbiotic micro-organisms.</li><li>A narrow finger -like tubular projection, the vermiform appendix which is a vestigial organ [small remnant of something that was once more noticeable], arises from the caecum.</li><li>The caecum opens into the colon. The colon is divided into three parts – an ascending, a transverse and a descending part. The descending part opens into the rectum which opens out through the anus.</li><li>No significant digestive activity occurs in the large intestine. The functions of large intestine are: absorption of some water, minerals and certain drugs; secretion of mucus which helps in adhering the waste (undigested) particles together and lubricating it for an easy passage.</li><li>The undigested, unabsorbed substances called faeces enters into the caecum of the large intestine through ileo-caecal valve, which prevents the back flow of the faecal matter. It is temporarily stored in the rectum till defaecation.</li></ul>

Question 36

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Layers of Alimentary canal?

Answer

A

<ul><li>wall of alimentary canal from oesophagus to rectum possesses four layers namely serosa, muscularis, sub-mucosa and mucosa.</li></ul>

<ol><li>Serosa is the outermost layer and is made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues.</li><li>Muscularis is formed by smooth muscles.</li><li>The submucosal layer is formed of loose connective tissues containing nerves, blood and lymph vessels. In duodenum, glands are also present in sub-mucosa.</li></ol>

<ul><li>The innermost layer lining the lumen of the alimentary canal is the mucosa. This layer forms irregular folds (rugae) in the stomach and small finger-like foldings called villi in the small intestine. Mucosal epithelium has goblet cells which secrete mucus that help in lubrication. Mucosa also forms glands in the stomach (gastric glands).</li></ul>

Question 37

Q

DIgestive glands?

Answer

A

<ol><li>Salivary glands</li><li>Liver</li><li>Pancreas</li></ol>

Question 38

Q

Salivary glands?

Answer

A

<ul><li>Saliva is mainly produced by three pairs of salivary glands, the parotids (cheek), the sub-maxillary (lower jaw) and the sub-linguals (below the tongue).</li><li>These glands situated just outside the buccal cavity secrete salivary juice into the buccal cavity.</li><li>The saliva breaks down the starch into sugars.</li></ul>

Question 39

Q

Liver?

Answer

A

<ul><li>The liver is a reddish brown gland situated in the upper part of the abdomen on the right side.</li><li>It is the largest gland in the body.</li><li>It secretes bile juice that is stored in a sac called the gall bladder.</li><li>The bile plays an important role in the digestion of fats.</li><li>It has two lobes. The hepatic lobules are the structural and functional units of liver containing hepatic cells.</li><li>The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gall bladder.</li><li>The duct of gall bladder (cystic duct) along with the hepatic duct from the liver, forms the common bile duct.</li><li>The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the sphincter of Oddi.</li></ul>

Question 40

Q

pancreas?

Answer

A

<ul><li>The pancreas is a large cream coloured gland located just below the stomach.</li><li>The pancreatic juice acts on carbohydrates and proteins and changes them into simpler forms.</li><li>The partly digested food now reaches the lower part of the small intestine where the intestinal juice [succus entericus] completes the digestion of all components of the food.</li><li>The pancreas is a compound (both exocrine and endocrine) elongated organ situated between the limbs of the ‘U’ shaped duodenum.</li><li>The exocrine portion secretes an alkaline pancreatic juice containing enzymes and the endocrine portion secretes hormones, insulin and glucagon.</li><li>contains amylase (breaks down carbohydrates), lypase (breaks down fats) and trypsin (breaks down proteins); thus pancreatic juice is called complete digestive juice</li></ul>

Question 41

Q

enzyme action in small intestine?

Answer

A

<ul><li>The pancreatic juice contains inactive enzymes – trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases and nucleases.<ul><li>Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active TRYPSIN, which in turn activates the other enzymes in the pancreatic juice.</li><li>these enzymes help convert protein, peptones and proteoses into dipeptides</li><li>lipase breaks down fats into di and monoglycerides and further into fatty acids and glycerol</li></ul></li><li>The bile released into the duodenum contains bile pigments (bilirubin and biliverdin), bile salts, cholesterol and phospholipids but no enzymes.</li><li>Bile helps in emulsification of fats, i.e., breaking down of the fats into very small micelles. Bile also activates LIPASES. Small amounts of lipases are secreted by gastric glands.</li></ul>

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