Introduction
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2.2 Definition, explanation, and functions of various parts
The human digestive system is a long muscular track consisting of mouth (Including teeth, tongue, salivary glands, etc.), pharynx, oesophagus, followed by stomach, small as well as the large intestine. The pancreas and gallbladder participate in the digestive process too.
Teeth
There are 8 “Incisors” that are present on the upper and lower jaws, 8 “Molar” help in grinding food, 4 “Canines” or pointed teeth outside the incisors. Moreover, 8 “Premolar” teeth are present in between molar and canines and 4 “Wisdom teeth” erupt after the age of 18. A total of 32 teeth helps in chewing the food and grinding them into smaller particles suitable for swallowing.
Tongue
The taste buds are present on tongues that are “melon-shaped”, other supporting cells and papillaehelp to understand sweet, sour, bitter, and salty tastes as well as generate sensations. It releases mucous and keeps the mouth moist (Hartenstein and Martinez, 2019).
Salivary Glands
A total of three pairs of salivary glands are present including Parotid, Submaxillary, and Sublingual. Two types of cells are present in salivary glands: “Serous and Mucous” secrete saliva and ptyalin enzymes which help in starch digestion.
Stomach
- The “J-shaped stomach” is one of the digestive organs consisting of serosa, muscular, sub mucous, as well as mucous layers from outside to inside. The digestive glands are located here that release digestive enzymes like pepsinogen.
- From the oxyntic cells, HCL is secreted to convert inactivated pepsinogen into pepsin, necessary for protein digestion. Other than digestion, small amounts of water, glucose, and alcohol are absorbed as well.
Small Intestine
- The same layers are present in the small intestine as well that has three parts- "Duodenum", "Jejunum" and "Ileum". It contains finger-like projections called villi and is almost 15-20 feet long.
- It secretes carbohydrate and protein digestive enzymes. Moreover, it plays an important role in the absorption of nutrients into the blood.
Pancreas
The pancreas is one of the primary digestive organs of the human body, secretes enzymes for digestion of carbohydrates, proteins, and fat.
Large Intestine
It is the last part of the human digestive system and has three parts- colon, rectum, and anus. However, it contains no villi and is associated with the release of excretory materials (Livovsky et al. 2020).
2.3 Analysis of different digestive enzymes
2.4 Summary of ptyalin enzyme
I have chosen the ptyalin enzyme for the practical experiment that helps to convert boiled starch into isomaltose, maltose, as well as maltotriose.
The Urinary System
The structural and functional unit kidney is “Nephron” that is responsible for the formation of urine in the body.
Glomerular filtration or ultrafiltration
- The blood enters into the “Bowman’s capsule” of the nephron with the help of afferent arterioles of the glomerulus and gets filtered. This Filtered blood is known as "Glomerular filtration".
- The filtration process is highly selective here and so only water and some other small molecules can pass this barrier.
- However, the rate of filtration is dependent on particle sizes, level of hydrostatic pressure, etc. GFR of Glomerular Filtration Rate is an important indicator of healthy kidney.
- The proteins and fats get filtered in this process too. It is a passive process where except the colloidal materials everything gets filtered.
- The basement membranes and podocytes are the components of glomeruli to act as barriers (Abdalla, 2020).
Tubular reabsorption
- Following glomerular filtration tubular reabsorption takes place where the excess amount of water as well as solutes gets reabsorbed by tubules and get back to the circulatory system.
- This helps to maintain the extracellular fluid balance and regulate salt and mineral levels.
- The reabsorption starts with “Proximal convoluted tubule”, followed by “Loop of Henle”, “Distal convoluted tubule” and finally collected by the “collecting duct” before excreted out in the form of urine.
- The sodium, potassium gets absorbed by primary and secondary active transport processes. Similarly the chlorine, bicarbonate ion, and creatinine get reabsorbed by a simple diffusion process.
- Glucose and amino acids are absorbed by facilitated diffusion processes and require the assistance of a carrier protein. Water gets reabsorbed by a passive mechanism, also known as osmosis.
Tubular Secretion
- Following reabsorption, some amount of hydrogen, potassium, creatinine, some other ions like ammonia, urea, etc. as well as drugs are secreted in this step (Segev et al. 2019).
- This is the final step of urine formation and with the glomerular filtrate these ions and compounds, known as “Urine” get eliminated from the body. Thus, Urine formation takes place.
6.2 Role of ADH
- The ADH or "Antidiuretic Hormone" facilitates the water reabsorption from the distal tubules as well as from the collecting duct.
- Most of the water gets absorbed in the proximal tubule by the "Obligatory Reabsorption Process" and in the distal tubules, by “Facultative Reabsorption Process”.
- ADH is produced by the hypothalamus and secreted from the posterior lobe of the pituitary, responsible for maintaining the water balance of the body.
- It binds to the receptors when the osmotic pressure is increased, meaning the body is lacking water or dehydrated.
- The feeling of thirst gradually increases as well. In this scenario, ADH reabsorbs water from distal tubules and the collecting ducts maintains the extracellular fluid levels and decreases the feeling of thirst.
- Thus, it prevents the excess amount of water loss from the body by urine and helps to regulate the blood pressure as well.
- Patients suffering from Diabetes Insipidus lacking in ADH which results in frequent urination and dehydration (CC Chatterjee's Human Physiology, 2018).
4.1 Male and female reproductive systems highlights
- The primary reproductive organ of males is a pair of testes that produce sperm and for females is a pair of ovaries that produce ovum.
- The secondary reproductive organs of males are “Epididymis”, “Vas deferens”, “Seminal vesicle”, as well as “Ejaculatory duct”. In addition, “Prostate gland”, “Cowper’s gland”, “urethra”, “scrotum” and “penis” are other secondary organs.
- The secondary reproductive organs of females are “Fallopian tubes”, “uterus”, “clitoris”, “vagina”, “mammary glands”, as well as “Bartholin’s gland”. Other than that, “Labia majora and labia minora” are other reproductive organs.
- After a boy hits puberty certain hormonal changes happen. A certain surge in testosterone secretion makes a boy gradually turn into a man. The body becomes muscular with broad shoulders, the development of a moustache and beard, the penis becomes larger along with a rough and deep voice. Hair appears in intimate areas.
- A surge in oestrogen and progesterone slowly turn a girl into a female. Her body becomes soft, vagina, and mammary glands enlarge. The menstruation gets started and the voice becomes high pitched. Hair grows in intimate areas as well (Ivell, 2017).
4.2 Structure and functions of reproductive organs
Male Reproductive Organs
Scrotum
The scrotum is a deep pigment pouch divided into two compartments, each containing testis. It has seven layers and maintains a 2-2.5 degrees Celsius lower temperature in that area.
Testes
- It is surrounded by three protective layers including “Tunica vaginalis”, “Tunica albuginea”, as well as “Tunica vasculosa”. It consists of around 200-300 lobules composed of germinal epithelial cells. These together form “Seminiferous tubules”.
- The exocrine function of the testes is to form spermatozoa in the seminiferous tubules, under the influence of GTH (Gonadotropin Hormone). The endocrine function is to secrete testosterone hormone.
Prostate gland
It lies around the urethra, close to the urinary bladder and covered with a vascular capsule. The secretion of this gland makes the urethra slippery enough to discharge the semen.
Cowper’s gland
This is a pair of “Pea-shaped glands” present below the prostate gland and it secretes a milky fluid that forms a significant part of the semen.
Female Reproductive Organs
Ovary
There are a pair of ovaries that are situated in the pelvic cavity, on both sides of the urethra. The main function of the ovaries is to produce eggs or ovules in the Graafian follicle and hormones such as oestrogen, progesterone, and relaxin as well.
Fallopian Tube
These tubules are attached with both the ovaries and are divided into four parts- “uterine part”, “isthmus”, “ampulla”, and “infundibulum”.
Uterus
- It is the muscular part of a woman's reproductive organs and is divided into “Fundus” or broad upper part, “Body”, the middle and “Cervix”
- There are three tissue layers present in the uterus and these are “Perimetrium”, “Myometrium”, and “Endometrium”. During menstruation, this endometrium layer undergoes different changes (Ivell and Anand-Ivell, 2021).
- It has a major role in the fertilisation and bearing of a child, and so its other name is "womb".
