Cell Biology: Intercellular Communication and Transport

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Questions and Answers

What characterizes ungated or leak channels?

They respond to mechanical stimuli.

They can only open with a change in voltage.

They require a specific ligand to open.

They are always open. (correct)

What is the primary function of neurohormones in the body?

To transport nutrients into the cells

To regulate temperature within the body

To release hormones into the bloodstream for distant target cells (correct)

To facilitate communication between neurons only

Which type of channel opens in response to changes in electrical potential?

Ligand-gated channels

Voltage-gated channels (correct)

Leak channels

Mechanically gated channels

Which mechanism requires no energy for the transport of substances?

Facilitated diffusion Signup and view all the answers

How do ligand-gated channels function?

They open in response to hormonal substances. Signup and view all the answers

Which type of diffusion occurs through the lipid bilayer of the cell membrane?

Simple diffusion only Signup and view all the answers

What triggers mechanically gated channels to open?

Physical pressure or deformation Signup and view all the answers

Which type of transport is facilitated by protein channels in cell membranes?

Facilitated diffusion without energy Signup and view all the answers

What characterizes passive transport mechanisms?

They can occur through both lipid bilayer and protein channels. Signup and view all the answers

What is a characteristic of simple diffusion through the lipid bilayer?

It is influenced by the solubility of substances in lipids. Signup and view all the answers

What role do intercellular communications play in multicellular organisms?

They enable cells to make life-sustaining exchanges with the external environment. Signup and view all the answers

Which type of intercellular communication involves physical contact between cells?

Direct communication through gap junctions Signup and view all the answers

What characterizes the action of paracrine chemical messengers?

They exert their effects on neighboring cells in the immediate environment. Signup and view all the answers

What distinguishes neurotransmitters from hormones in terms of their action range?

Neurotransmitters act on local target cells, while hormones act systemically. Signup and view all the answers

What is the main function of hormones in the context of intercellular communication?

To transmit signals to other sites in the body via the bloodstream. Signup and view all the answers

Study Notes

Intercellular Communication

Most cells are not in direct contact with the external environment.
Direct communication: Cells are physically connected through structures like gap junctions.
Indirect communication: Cells use extracellular chemical messengers, which are secreted by cells and act on target cells to exert their effects.
Paracrine messengers: These messengers act locally on neighboring cells.
Neurotransmitters: Released by nervous cells in response to electrical signals. They act on nearby target cells, including other neurons, muscles, and glands.
Hormones: Long-range messengers secreted by endocrine glands into the bloodstream. They travel to distant target cells to elicit responses.
Neurohormones: Hormones released by neurosecretory neurons into the blood.

Transport Across Cell Membrane

Cells need to exchange substances with their environment.
Passive transport: Movement of substances along concentration or electrical gradients (downhill). It does not require energy.
- Simple diffusion: Substances move directly through the lipid bilayer or protein channels of the cell membrane.
- Facilitated diffusion: Substances are transported across the membrane with the help of carrier proteins.
Active transport: Movement of substances against concentration, electrical, or electrochemical gradients (uphill). It requires energy.
- Primary active transport: Energy is directly obtained from the breakdown of ATP.
- Secondary active transport: Energy for the movement of one substance is obtained from the movement of a second substance, often coupled through a carrier protein.

Homeostasis

Homeostasis: Maintaining a stable internal environment within a narrow range, despite external fluctuations, is vital for life.
Components of a homeostatic control system:
- Sensors (receptors): Detect changes in the internal environment.
- Control center: Receives information from sensors and sends out commands to effectors.
- Effectors: Carry out the adjustments to correct deviations from the set point.
Negative feedback: The response opposes the initial stimulus, bringing the system back towards a set point.
Positive feedback: The response amplifies the initial stimulus.

Examples of Homeostatic Mechanisms

Negative feedback examples: Regulation of blood pressure, body temperature, and blood glucose levels.
Positive feedback examples: Blood coagulation, labor, and membrane excitation.

Homeostasis Disturbance Example: Fever (Pyrexia)

Pyrogens: Substances that trigger fever. They can be released by bacteria or from degenerating tissues.
Macrophages: These immune cells engulf pyrogens and release interleukin-1 (an endogenous pyrogen).
Prostaglandins (PGE2): Interleukin-1 stimulates the formation of prostaglandins, which raise the set point of the body's internal thermostat.
The higher set point triggers heat production mechanisms, leading to a fever.

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Description

Explore the mechanisms of intercellular communication, including direct and indirect methods like gap junctions, paracrine messengers, neurotransmitters, and hormones. Additionally, learn about the processes involved in transport across the cell membrane, focusing on passive transport and its significance in cellular functions.