1.explain why people have different skin color
2.with examples highlight five function of plasma membrane protein
3.list one function of ant four organelles of human cell you know
4.with regard to transport processes in the human body explain how human immunodeficiency virus (HIV) gets into and out of the host cell
5.explain how action potential is generated and transmitted
6.how does skin necrosis come about
1. People have different skin color due to variations in the amount and type of melanin, a pigment that determines the color of skin, hair, and eyes. Melanin is produced by specialized cells called melanocytes present in the epidermis. The amount of melanin produced by these cells is regulated by various factors, including genetics, exposure to sunlight, and hormones.
Example: People living closer to the equator have more melanin in their skin, which provides protection against harmful UV radiation. On the other hand, people living in regions farther from the equator have less melanin, resulting in lighter skin color.
2. Functions of plasma membrane proteins:
- Transport Proteins: Facilitate the movement of substances across the plasma membrane. For example, channels and carriers help transport ions, nutrients, and wastes across the cell membrane.
- Receptor Proteins: Bind to specific molecules, such as hormones or neurotransmitters, to initiate specific cellular responses.
- Enzymatic Proteins: Catalyze various biochemical reactions at the cell surface. They may be involved in signal transduction or cell communication.
- Cell Adhesion Proteins: Help cells adhere to neighboring cells or extracellular matrix, contributing to cell cohesion and tissue integrity.
- Cell Recognition Proteins: Play a role in immune responses and cell-cell communication by differentiating between the body's cells and foreign invaders.
3. Functions of organelles in human cells:
- Nucleus: Controls the cell's activities and stores genetic information in the form of DNA.
- Mitochondria: Generate energy in the form of ATP through cellular respiration.
- Golgi Apparatus: Modifies, sorts, and packages proteins for transport to specific destinations within or outside the cell.
- Endoplasmic Reticulum: Involved in protein synthesis, lipid metabolism, and detoxification.
4. Human Immunodeficiency Virus (HIV) enters and exits the host cell through various transport processes. HIV primarily infects immune cells called CD4+ T cells.
Entry: HIV uses glycoproteins on its outer envelope called gp120 to bind to CD4 receptors on the surface of CD4+ T cells. This binding is followed by fusion of the viral envelope with the host cell membrane, allowing the viral RNA and enzymes to enter the cell.
Exit: After viral replication within the host cell, newly formed HIV particles are released. This process involves budding, where the viral proteins and RNA are surrounded by a piece of the host cell membrane. This particle, called a virion, is then released from the host cell and can infect other cells.
5. Action potential is generated and transmitted in the following manner:
- Resting Potential: Neurons have a resting membrane potential, primarily maintained by the movement of ions across the plasma membrane through ion channels. At rest, the inside of the neuron is negatively charged compared to the outside.
- Depolarization: When a stimulus (chemical or electrical) reaches a threshold, sodium channels in the neuron's membrane open, allowing sodium ions to rush in, depolarizing the membrane. This depolarization triggers an action potential.
- Action Potential: The depolarization opens more sodium channels, resulting in a self-propagating electrical impulse along the neuron's axon. This is the action potential characterized by a rapid change in membrane potential, from negative to positive. Potassium channels open slightly after the sodium channels, contributing to repolarization.
- Repolarization: After the action potential, potassium channels open, allowing potassium ions to rush out of the neuron, restoring the negative membrane potential. This repolarization phase is necessary to reset the neuron for subsequent action potentials.
6. Skin necrosis occurs when there is insufficient blood supply or damage to the skin tissue, leading to cell death. It can be caused by various factors, including:
- Ischemia: Reduced blood flow to the skin due to blockage or damage to blood vessels can result in tissue death.
- Infection: Severe infections, especially bacterial infections, can damage and destroy skin cells, leading to necrosis.
- Injury: Severe trauma, burns, or excessive pressure can cause the skin tissue to become damaged and deprived of blood supply, resulting in necrosis.
- Autoimmune disorders: Certain conditions, like vasculitis or systemic lupus erythematosus, can result in immune-mediated damage to the skin, leading to necrosis.
2. With your understanding of the feedback loop, explain the physiology of normal labour (normal child birth) (10 marks)
3. Describe how plasma membrane of the human cell maintains balance of:
a. Glucose (5 marks)
b. Potassium (5 marks)
6. Distinguish cells that line the small intestines and those that line stomach (10 marks)
7. Indicating examples, identify four types of human tissues (20 marks)
8. Explain how urinary bladder holds urine
2. The physiology of normal labor involves a complex feedback loop between the mother's body and the fetus. Here is a simplified explanation:
- Initiation of Labor: As the fetus reaches maturity, it releases signaling molecules called fetal prostaglandins, which stimulate the mother's uterus. This triggers the release of oxytocin, a hormone that causes contractions of the uterine muscles.
- Positive Feedback Loop: The contractions of the uterus during labor stimulate further release of oxytocin from the mother's pituitary gland. This creates a positive feedback loop, increasing the intensity and frequency of contractions.
- Cervical Dilation: The contractions help to thin and open the cervix or the entrance to the uterus, allowing the fetus to pass through the birth canal.
- Delivery of the Fetus: The contractions continue, pushing the fetus downward and out through the birth canal. The mother may voluntarily assist by pushing during this stage.
- Delivery of the Placenta: After the fetus is delivered, the mother continues to have contractions, which help to expel the placenta from the uterus.
- Hormonal Regulation: Throughout this process, hormones such as progesterone and relaxin play a role in relaxing the ligaments and facilitating the coordination of labor.
3a. Glucose balance in the plasma membrane:
- Glucose entry: Glucose transporter proteins, specifically GLUT proteins, facilitate the transport of glucose across the plasma membrane into the cell. These transporters act in response to glucose concentration gradients and insulin signaling.
- Glucose exit: Glucose can exit the cell through facilitated diffusion using the same GLUT transporter proteins, maintaining a balance between intracellular and extracellular glucose concentrations.
- Insulin regulation: Insulin, produced by the pancreas, regulates glucose transporters' activity on the plasma membrane. Insulin promotes increased glucose uptake by increasing the number and activity of GLUT proteins on the cell surface.
- Energy homeostasis: The plasma membrane proteins also regulate glucose balance by ensuring the appropriate uptake and utilization of glucose for energy production within the cell.
3b. Potassium balance in the plasma membrane:
- Potassium channels: Plasma membrane proteins, such as potassium channels, allow the movement of potassium ions across the membrane. These channels help to maintain the balance of potassium inside and outside the cell.
- Active transport: The sodium-potassium pump, a protein located in the plasma membrane, actively pumps potassium ions into the cell and sodium ions out of the cell. This process helps establish the electrochemical gradient necessary for cellular functions.
- Concentration gradient: The movement of potassium ions through potassium channels is regulated by the concentration gradient of potassium. This gradient is maintained through the sodium-potassium pump's continuous activity.
- Cellular excitability: Potassium channels also regulate the resting membrane potential of cells, creating and maintaining the negative charge within the cell. This is essential for proper electrical signaling and cellular excitability.
6. Cells lining the small intestines and those lining the stomach have distinct characteristics:
- Small Intestine:
- Absorptive Cells (Enterocytes): These cells have microvilli on their apical surface, increasing their surface area for nutrient absorption. They contain digestive enzymes and transporters to absorb nutrients into the bloodstream.
- Goblet Cells: These cells secrete mucus, which protects the small intestine lining and aids in the movement of food.
- Endocrine Cells: These cells secrete hormones such as cholecystokinin (CCK) and secretin, which regulate digestion and nutrient absorption.
- Stomach:
- Mucous Cells: These cells secrete mucus, which protects the stomach lining from stomach acid and aids in the digestion of food.
- Parietal Cells: These cells secrete hydrochloric acid (HCl) and intrinsic factor. HCl helps in the breakdown of food and intrinsic factor assists in vitamin B12 absorption.
- Chief Cells: These cells secrete pepsinogen, an inactive enzyme that is later activated to pepsin to break down proteins.
- Endocrine Cells: Stomach lining contains endocrine cells that secrete hormones such as gastrin, which stimulates the production of gastric acid.
7. Four types of human tissues:
- Epithelial Tissue: Found in skin, lining of organs, and glands. Examples include skin epithelium, lining of the intestines, and sweat glands.
- Connective Tissue: Supports and connects different parts of the body. Examples include bone, cartilage, tendons, and adipose tissue.
- Muscle Tissue: Responsible for movement. Examples include skeletal muscles, smooth muscles in organs, and cardiac muscles in the heart.
- Nervous Tissue: Coordinates and transmits signals within the body. Examples include neurons and glial cells in the brain and spinal cord.
8. The urinary bladder holds urine through a combination of structural and physiological mechanisms:
- Structure: The bladder is made up of elastic muscular walls, mainly smooth muscle known as the detrusor muscle. This muscle can stretch to accommodate urine and contract to expel it during micturition (urination).
- Sphincters: The urinary bladder has two sphincters. The internal urethral sphincter, a ring of smooth muscle at the bladder's base, helps maintain continence by providing involuntary control over urine flow. The external urethral sphincter, made up of skeletal muscle, provides voluntary control and can be consciously relaxed to initiate urination.
- Neural Control: Sensory nerves in the bladder wall detect the filling of urine, sending signals to the spinal cord and brain. When the bladder is sufficiently full, motor nerves stimulate the detrusor muscle to contract and the internal sphincter to relax, initiating urination. Conscious control can then be exerted to further release urine through relaxation of the external sphincter.
1. People have different skin colors due to the pigment called melanin, which is produced by cells called melanocytes. The amount and type of melanin produced determine the skin color. People with more melanin have darker skin, while those with less melanin have lighter skin. The differences in skin color are largely due to a combination of genetic factors and adaptations to different environments. For example, people living closer to the equator, where there is more intense sunlight, tend to have darker skin to protect against harmful UV radiation.
2. Examples of functions of plasma membrane proteins include:
a) Transport proteins: These proteins facilitate the movement of molecules across the membrane. For example, glucose transporters help facilitate the uptake of glucose into cells.
b) Receptor proteins: These proteins bind to specific molecules, such as hormones or neurotransmitters, and initiate a cellular response. For example, insulin receptors bind to insulin, which triggers the uptake of glucose by cells.
c) Enzymes: Some proteins embedded in the plasma membrane act as enzymes, catalyzing specific biochemical reactions. For example, the enzyme adenylate cyclase converts ATP to cyclic AMP as part of cellular signaling pathways.
d) Cell adhesion proteins: These proteins mediate cell-to-cell interactions and help maintain tissue structure. For example, integrins are involved in cell adhesion and signaling.
e) Channel proteins: These proteins form channels that allow specific ions or molecules to pass through the membrane. For example, ion channels help facilitate the movement of sodium, potassium, and calcium ions across the membrane.
3. Functions of four organelles in human cells:
a) Nucleus: The nucleus contains genetic material (DNA) and controls cellular activities by regulating gene expression.
b) Mitochondria: Mitochondria are responsible for generating energy in the form of ATP through cellular respiration.
c) Endoplasmic reticulum: The ER is involved in protein synthesis, lipid metabolism, and the storage and release of calcium ions.
d) Golgi apparatus: The Golgi apparatus modifies, sorts, and packages proteins and lipids for transport to their final destinations within or outside the cell.
4. HIV enters host cells through a process called membrane fusion. The virus attaches to the target cell's surface using its viral envelope glycoprotein called gp120, which binds to the CD4 receptor on the host cell membrane. This attachment triggers conformational changes in the gp120 protein, exposing a region called the co-receptor binding site. HIV can bind to one of two co-receptors: CCR5 or CXCR4.
Once the viral envelope and host cell membranes come into close proximity, a fusion peptide on the viral envelope glycoprotein gp41 inserts into the host cell membrane. This allows the fusion of the viral envelope with the host cell membrane, releasing the viral contents into the host cell.
To exit the host cell, newly synthesized viral particles assemble and bud from the host cell membrane. The viral protease enzyme cleaves the precursor viral proteins, resulting in the formation of mature viral particles that can infect other cells.
5. Action potentials are generated and transmitted in neurons. They are electrical signals that allow communication between different parts of the nervous system. Here is a simplified summary of how an action potential is generated and transmitted:
- Resting state: The neuron is at rest, with a negative membrane potential. The inside of the neuron is more negatively charged compared to the outside.
- Depolarization: When a stimulus reaches a threshold, ion channels in the neuron's membrane open, allowing sodium ions to rush into the neuron. This depolarizes the membrane, making it more positive.
- Rising phase: The influx of sodium ions causes a rapid depolarization known as the rising phase of the action potential. This leads to a positive feedback loop, as the depolarization opens more sodium channels, causing more sodium ions to enter the neuron.
- Falling phase: After reaching its peak, the membrane potential begins to repolarize. Potassium channels open, allowing potassium ions to leave the neuron, which makes the membrane potential more negative again.
- Undershoot: For a brief period, the membrane potential becomes more negative than the resting state, known as the hyperpolarization or undershoot.
- Refractory period: The neuron enters a refractory period during which it is less likely to generate another action potential.
Action potentials are transmitted along the neuron's axon through a process called saltatory conduction. The depolarization at one section of the axon triggers the opening of adjacent voltage-gated sodium channels, propagating the action potential down the axon.
6. Skin necrosis occurs when there is tissue death in the skin. It can be caused by various factors, including:
- Severe trauma: Severe injuries, such as burns, deep wounds, or crushing injuries, can cause damage to the blood vessels supplying the skin. Without proper blood supply, the skin cells do not receive enough oxygen and nutrients, leading to necrosis.
- Infections: Certain bacterial or fungal infections can cause skin necrosis. These infections can cause tissue damage and impair blood flow to the affected area, resulting in necrosis.
- Vascular disorders: Conditions that affect blood vessels, such as vasculitis or blood clotting disorders, can disrupt blood flow to the skin and lead to necrosis.
- Certain medications or treatments: Some medications, such as certain chemotherapy drugs, can cause skin necrosis as a side effect. Radiation therapy can also damage skin tissues and cause necrosis in the treated area.
Skin necrosis should be evaluated and treated by a medical professional, as it can lead to further complications if not addressed promptly.