Introduction to Physiology and Cell Membrane

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Questions and Answers

What is the primary function of the cell membrane?

To serve as a barrier around the cell (correct)

To facilitate protein synthesis

To generate energy for the cell

To store genetic information

Which of the following components is found in a cell membrane?

Chloroplasts

Mitochondria

Phospholipids (correct)

Nucleolus

Homeostasis in the body is primarily concerned with maintaining which of the following?

The size of individual cells

A dynamic internal environment (correct)

A constant external environment

The function of all organelles

Which type of feedback mechanism promotes stability in the body?

Negative feedback Signup and view all the answers

What is the composition of the cytosol in a cell?

A gelatinous fluid Signup and view all the answers

Which organelles are typically solitary in a cell?

Nucleus Signup and view all the answers

What do ion channels and transport proteins in the cell membrane regulate?

The permeability of the membrane Signup and view all the answers

What is the role of cholesterol in the cell membrane?

To provide structural integrity between phospholipids Signup and view all the answers

What is the main function of the endocrine system?

To regulate activities requiring duration via hormones Signup and view all the answers

What role do receptors play in homeostatic control systems?

They detect changes in a controlled condition Signup and view all the answers

Which of the following is an example of negative feedback?

Blood pressure responsiveness to loss of blood Signup and view all the answers

What characterizes positive feedback mechanisms?

They exaggerate changes away from a set-point Signup and view all the answers

Which system is primarily responsible for rapid bodily responses?

Nervous system Signup and view all the answers

What is one of the key functions of the urinary system?

To excrete wastes and excess substances Signup and view all the answers

What is the overall goal of homeostasis?

To maintain stability in the body’s environment Signup and view all the answers

How does the skin contribute to homeostasis?

As a barrier against pathogens and in vitamin D activation Signup and view all the answers

What is the primary function of the phospholipid bilayer in cellular membranes?

It serves as a selective barrier between the ICF and ECF. Signup and view all the answers

Which of the following statements about membrane proteins is true?

Receptors alter cell functions by binding neurotransmitters or hormones. Signup and view all the answers

How does homeostasis contribute to cell survival?

By maintaining stable internal conditions necessary for cell function. Signup and view all the answers

Which parameter is NOT typically regulated by homeostatic mechanisms in the internal environment?

Topography of the surrounding environment Signup and view all the answers

Which of the following is a function of membrane carbohydrates?

They act as receptors for certain hormones. Signup and view all the answers

What role do pumps play in membrane proteins?

Transporting ions uphill using energy (ATP). Signup and view all the answers

Which of the following factors must be maintained for optimal homeostasis?

pH level of 7.4 Signup and view all the answers

What is the primary function of ion channels in membrane proteins?

To facilitate the passive passage of specific ions. Signup and view all the answers

Which scenario exemplifies a positive feedback mechanism?

Blood clotting process Signup and view all the answers

What characterizes a feedforward response?

It anticipates a change in a regulated variable Signup and view all the answers

Which of the following statements about positive feedback is true?

It can lead to a vicious cycle if unchecked. Signup and view all the answers

Which of the following is an example of a physiological response that occurs through feedforward mechanisms?

Secretion of insulin after a meal Signup and view all the answers

How does positive feedback differ from negative feedback mechanisms?

Positive feedback usually ends with a specific outcome. Signup and view all the answers

Study Notes

What is Physiology?

The study of the vital functions of living organisms, including their organs, cells, and molecules
Focuses on how the human body functions, which depends on the individual organ systems, component cells, and interactions between subcellular organelles and molecules.
Considered the foundation for many biological sciences.

Structure of the Cell Membrane

All cells are enveloped by a plasma membrane.
The cell membrane is semi-permeable, allowing some substances to pass through it while excluding others.
Its permeability is greatly varied due to the presence of regulated ion channels and transport proteins.
The plasma membrane maintains a unique composition for the intracellular fluid, which is different from the extracellular fluid.
Membrane Lipids:
- Major membrane lipids are phospholipids, with few cholesterol molecules present in between the phospholipid bilayer.
- Functions: forms a barrier around the cell, serves as a selective barrier for substance passage, fluidity due to phospholipid and cholesterol movement allowing shape changes (muscle cells contracting).
Membrane Proteins:
- Function:
  - Ion channels: allow passage of ions into and out of the cell (downhill transport).
  - Carriers: facilitate downhill transport.
  - Pumps: facilitate uphill transport using energy (ATP).
  - Receptors: bind to neurotransmitters or hormones to alter cell functions.
  - Enzymes: catalyze specific chemical reactions.
  - Cell adhesion molecules (CAM): hold cells together (intercellular junction).
Membrane Carbohydrates on the outer membrane:
- Types: glycoproteins and glycolipids.
- Functions:
  - Act as receptors for certain hormones.
  - Serve as self-identity markers for cell identification and interaction (cell recognition molecules), involved in immune reactions.
  - Act as antigen-like markers, e.g., blood group markers.

Homeostasis

The maintenance of a relatively stable (dynamic steady state) internal environment (ECF).
Essential for the survival and function of all cells.
Cells and tissues function efficiently only when internal conditions are properly maintained.
Homeostasis is not unlimited, as the body can resist changes in the internal environment to a variable range and time. Almost all diseases are a failure of homeostasis.
Body cells are bathed in a fluid medium (watery internal environment).

Factors in the Internal Environment that must be Homeostatically Maintained

pH: 7.4.
Blood Volume: 5 L.
Blood Pressure: 120/80 mmHg.
Temperature: 37 ◦C.
Partial Pressure of Oxygen (O2): 100 mmHg in arterial blood.
Partial Pressure of Carbon Dioxide (CO2): 40 mmHg in arterial blood.
Concentration of water, salt, and other electrolytes.
Concentration of nutrients and waste products.

Body Systems that Contribute to Homeostasis

Circulatory System: Continuous movement of blood in the circulatory system, transporting nutrients, O2, CO2, wastes, and electrolytes.
Respiratory System: Blood passing through the lungs picks up oxygen and releases carbon dioxide into the alveoli, maintaining oxygen and carbon dioxide levels in the blood.
Digestive System: Digests and absorbs nutrients.
Nervous System (rapid): Controls and coordinates bodily activities requiring rapid responses, detecting and initiating reactions to changes in the external environment,
Endocrine System (slow): Regulates activities requiring duration rather than speed through hormone secretion, controls nutrient concentration, and adjusts kidney function to control internal environment volume and electrolyte composition.
Musculoskeletal System: Coordinates movements and stabilizes the human body.
Immune System: Defense mechanism against infection.
Skin: Biological barrier, prevents entry of foreign bodies or particles, plays a role in vitamin D activation.
Urinary System: Excretes wastes, excess water, electrolytes, and hydrogen.

Components of Homeostatic Control Systems

Feedback: Responses made after a change has been detected.
- Receptor (sensor, detector): Structures that monitor a controlled condition and detect changes (detect stimuli).
- Afferent Pathway: Neural or hormonal pathway carrying information from the receptor to the control center.
- Control Center (integrator): Compares the detected variable to the set point and determines the appropriate effector response.
- Efferent Pathway: Neural or hormonal pathway conveying the control center's instructions to the effector.
- Effector: Receives orders from the control center, producing a response that restores the controlled condition (muscles or glands).

Types of Feedback (Control) Systems:

Negative Feedback: A response that opposes the initial change.
- The majority of the body's compensatory homeostatic mechanisms function by negative feedback.
- Examples: Blood pressure changes, body temperature changes, blood glucose changes, blood gas changes.
Positive Feedback: Change is driven further away from the original set point (exaggerates the change).
- Temporary and has some physiological importance.
- Examples: Normal childbirth, blood clotting, stress.
Feedforward: Responds in anticipation of a change in a regulated variable.
- Less frequently used.
- Examples: Increased saliva due to sight, smell, or thought of food; rise in respiration before exercise; shivering before diving into cold water; increased insulin secretion due to food presence in the digestive tract, preventing excessive blood glucose rise after a meal.

Examples:

Negative Feedback (90%):

Blood Pressure Changes: A drop in blood pressure is detected by receptors, which signal the brain (control center). The brain then signals the heart (effector) to beat faster and blood vessels (effector) to constrict, increasing blood pressure.
Body Temperature Changes: A rise in body temperature triggers sweating, causing heat loss and decreasing body temperature.
Blood Glucose Changes: Rising blood glucose levels stimulate insulin release from the pancreas, promoting glucose uptake by cells and lowering blood glucose levels.

Positive Feedback:

Childbirth: Stretch receptors in the uterine wall send signals to the brain, releasing oxytocin into the bloodstream. Oxytocin stimulates more forceful uterine contractions, leading to more stretching and more hormone release, pushing the cycle forward until the baby is born.

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Description

Explore the fundamentals of physiology, focusing on the vital functions of living organisms and the structure of the cell membrane. This quiz covers the importance of organ systems, cell components, and the unique characteristics of the plasma membrane. Test your understanding of these essential biological concepts.