The human body is composed of approximately 50-60% total body water, with men having a higher percentage of water at around 60%. This means that a 70Kg man would have approximately 42 litres of total body water.

This water is divided into two main categories: extracellular fluid and intracellular fluid. Extracellular fluid makes up one third of the total body water and is further divided into four subcategories: plasma, interstitial fluid, lymph, and transcellular fluid.

Plasma makes up 3.5 litres, interstitial fluid makes up 8.5 litres, while lymph and transcellular fluid each make up 1.5 litres. The remaining two thirds of the total body water is intracellular fluid.

It is important to note that the concentration of electrolytes, such as potassium, in the extracellular fluid is crucial for maintaining proper bodily function. In fact, an extracellular fluid concentration of 12 mmol/L of potassium is incompatible with life.

The body’s fluid composition is essential for maintaining overall health and wellness.

Cirrhosis: End-Stage Fibrosis of the Liver

Cirrhosis is a condition that describes the changes that occur in the liver when it reaches end-stage fibrosis. This happens due to chronic inflammation that leads to the death of liver cells or hepatocyte apoptosis. Initially, the dead cells are replaced by new ones through hepatocyte regeneration. However, in cases of chronic inflammation, activated stellate cells deposit fibrous tissue in the liver, leading to the formation of large bands that stretch between portal tracts. These tracts are also expanded with fibrosis, and areas of hepatocyte regeneration occur, forming nodules. Unfortunately, at this stage, the normal relationship between hepatocytes, portal triads, and central vein is lost, leading to poor drainage of portal blood through the liver. This results in increased back-pressure and portal hypertension. It is important to note that these features alone do not necessarily indicate cirrhosis.

The Retina and its Cell Types

The retina is composed of various types of cells, with the ganglion cell layer being the most superficial layer that is first exposed to light. Ganglion cells are the only neurons present in the retina, and they have an axon that extends centrally to form the optic nerve. These cells form synapses with bipolar cells, which are located deeper in the retina. Bipolar cells, in turn, synapse with photoreceptors, which are situated in the deepest layer of the retina. Supporting cells such as horizontal cells and amacrine cells are positioned between the other cells.

Photoreceptors play a crucial role in the retina by absorbing light and generating electrical impulses that travel through the optic nerve to the occipital lobe, where photographic images are created. The retina’s complex structure and the interactions between its various cell types enable us to see the world around us.

Anatomy and Function of the Adrenal Glands

The adrenal glands are composed of two distinct parts: the outer cortex and the inner medulla. The adrenal cortex is responsible for producing the body’s steroid hormones and is divided into three layers. The outermost layer, the zona glomerulosa, produces mineralocorticoids such as aldosterone. The middle layer, the zona fasciculata, produces glucocorticoids like cortisol. The innermost layer, the zona reticularis, produces androgens such as DHEA and androstenedione.

On the other hand, the adrenal medulla is made up of enterochromaffin cells, which are neural crest derivatives that secrete catecholamines. The adrenal gland is covered by a fibrous capsule that contains fibroblasts. The adrenal gland plays a crucial role in regulating various bodily functions, including blood pressure, metabolism, and stress response.

Carcinoma in Situ: A Non-Invasive Tumor

A carcinoma in situ is a type of tumor that appears malignant under microscopic examination but has not yet invaded through the basement membrane. This membrane is a crucial feature that defines malignancy, and without it, the tumor cannot metastasize. Therefore, local resection is often curative. The cells that make up a carcinoma in situ typically exhibit high-grade dysplasia, which means they have all the characteristics of malignancy.

It’s important to note that benign growths do not invade through the basement membrane, and low-grade dysplasia alone is not enough to define a carcinoma in situ. Additionally, an inherited mutation in an oncogene or tumor suppressor gene can increase the risk of developing malignancy, but it does not necessarily result in a carcinoma in situ.

Overall, a carcinoma in situ is a non-invasive tumor that has the potential to become malignant if it invades through the basement membrane. However, with proper treatment, it can often be cured before it becomes a more serious issue.

Dysplasia and its Association with Malignancy

Dysplasia refers to the cellular changes that occur during the development of malignancy. The degree of dysplasia in a cell is directly proportional to its likelihood of being found in an invasive cancer. Cells with higher-grade dysplasia have more genetic abnormalities than those with low-grade dysplasia.

Progressive dysplasia is characterized by variations in the appearance of cells and their nuclei, which is not typical in most tissues where cells appear similar. The nuclei of dysplastic cells are larger, and there is an increase in the number of nucleoli. The Ki67 index is a marker of proliferation, and a higher Ki67 index indicates a higher rate of cell turnover.

In most tissues, mitoses are rare, but malignant tissues made up of dysplastic cells show visible mitoses. dysplasia and its association with malignancy is crucial in the early detection and treatment of cancer.

Cilia, Flagella, and Microvilli: Cellular Projections with Unique Functions

Cilia, flagella, and microvilli are cellular projections that serve different functions in various cells. Cilia are hair-like structures made up of microtubules and dynein proteins. They can be either immotile or motile, with immotile cilia used for sensory transduction and attachment to underlying tissues, while motile cilia beat rhythmically to move fluid over the surface of cells or confer motility to cells. Cilia are found in the respiratory tract and Fallopian tube epithelium.

Flagella, on the other hand, are longer projections that are classified as a type of cilium. Spermatozoa have a long flagellum that has a similar internal structure to a cilium but is much longer and is used for motility.

Microvilli are folds of the cell membrane that increase the surface area for absorption. They are found in cells such as ileal enterocytes, which are responsible for nutrient absorption in the small intestine.

In summary, cilia, flagella, and microvilli are cellular projections that serve unique functions in different cells. While cilia can be either immotile or motile, flagella are longer and used for motility, and microvilli increase surface area for absorption.

The Structure of the Glomerulus

The glomerulus is composed of glomerular capillaries that are lined by a basement membrane and podocyte processes. Podocytes are connected to the epithelial cells of Bowman’s capsule, which are then connected to the cells of the proximal convoluted tubule. Supporting cells called mesangial cells are located between the capillary endothelial cells and podocytes. These cells produce the extracellular matrix that supports the structure of the glomerulus and remove dead cells through phagocytosis. Additionally, mesangial cells may play a role in regulating glomerular blood flow. Overall, the glomerulus is a complex structure that plays a crucial role in the filtration of blood in the kidneys.

Different Types of Cells in the Body

Mesothelial cells are a type of flat epithelial cells that are responsible for lining cavities in the body. These cells can be found in the parietal and visceral pleura, peritoneum, tunica vaginalis, and pericardium. They secrete a small amount of lubricant fluid that allows the parietal and visceral layers to move against each other with low friction. However, mesothelial cells are also known for their development into mesothelioma, a malignant tumor that is strongly associated with asbestos exposure and has a poor prognosis.

Endothelial cells, on the other hand, are responsible for lining blood vessels. Fibroblasts are cells that secrete extracellular matrix, which is important for tissue repair and wound healing. Mesangial cells are supporting cells of the glomerular capillaries, which are responsible for filtering blood in the kidneys. Lastly, goblet cells are mucus-secreting cells that can be found throughout the body, particularly in the respiratory and digestive tracts.

Overall, the body is made up of various types of cells that have different functions and play important roles in maintaining overall health and well-being.

Types of Cartilage

Hyaline cartilage is a type of cartilage that is firm and is composed of type II collagen. It is found in various parts of the body such as the nose, the cartilaginous rings of the trachea, the foetal skeleton, and lines synovial joints in a specialized form known as articular cartilage. Articular cartilage has a more regular arrangement of collagen fibers and slightly more elastin, which makes it less frictional and facilitates the movement of synovial joints.

Fibrocartilage, on the other hand, is made up of type I collagen and is much more solid. It is used to hold bones together, such as in the pubic symphysis. Lastly, elastic cartilage has a rich elastin content and forms the pinna of the ear.