Physiology - Epithelia - Quiz, Flashcards & Trivia

1. Define the properties of epithelia.

Epithelia have no specific properties

- Connected cells barrier/ compartment
-polarity
- different protein expression
- different epithelia, different behaviour

Epithelia have the same protein expression regardless of type

Epithelia are only found in plants

Epithelia are characterized by the properties of connected cells forming a barrier, compartment-polarity, different protein expression, and varied behavior based on the type of epithelia.

Explanation

Epithelia are characterized by the properties of connected cells forming a barrier, compartment-polarity, different protein expression, and varied behavior based on the type of epithelia.

2. What is a tight junction?

A junction in plants that aids in photosynthesis and nutrient absorption.

A type of junction found in muscles that allows for flexibility and movement.

A junction in nerve cells that helps transmit electrical impulses.

A junction in the epithelial cell that separates the apical from the basolateral membrane side (cell polarisation).
- It is an important part of the paracellular pathway and constrains/forces the free diffusion of solutes and fluids (claudins)

Tight junctions are specifically found in epithelial cells and play a crucial role in maintaining cell polarity and regulating the movement of solutes and fluids between cells. They are not found in muscles, nerve cells, or plants for photosynthesis.

Explanation

Tight junctions are specifically found in epithelial cells and play a crucial role in maintaining cell polarity and regulating the movement of solutes and fluids between cells. They are not found in muscles, nerve cells, or plants for photosynthesis.

3. What is a gap junction?

A type of junction that helps with muscle contraction

A junction in the epithelia that connects cytoplasmic compartments of cells. It allows the exchange of small molecules between cells (cell communication). In some cases, gap junctions build electrical connections (electrical synapses, heart)
- gap junctions form intercalated discs e.g in the SA node

A type of junction that stores excess nutrients

A type of junction found only in plant cells

Gap junctions are specific cellular structures that facilitate communication and exchange of molecules between adjacent cells. They are not involved in muscle contraction, exclusive to plant cells, or used for nutrient storage.

Explanation

Gap junctions are specific cellular structures that facilitate communication and exchange of molecules between adjacent cells. They are not involved in muscle contraction, exclusive to plant cells, or used for nutrient storage.

4. What are desmosomes?

A type of hormone produced by the adrenal glands

A structure found in plant cells responsible for photosynthesis

A junction in the epithelia cell that connects cells tightly via cadherins. Cadherins are connected to intermediate filaments that organise intra-cellular filaments (stabilisation). Epithelia exposed to physical stress are often connected via many desmosomes.

A type of enzyme involved in protein digestion

Desmosomes are specific cell junctions found in epithelial cells, serving to connect cells tightly and provide structural integrity particularly in tissues exposed to physical stress.

Explanation

Desmosomes are specific cell junctions found in epithelial cells, serving to connect cells tightly and provide structural integrity particularly in tissues exposed to physical stress.

5. What is an adhering junction?

An adhering junction is a junction that provides information about the nature and proximity of cells via cadherins. It is the prerequisite for the epithelial organisation and the apical /basolateral cell polarity. In epithelial tumours, the loss of adhering junction cadherins may be the reason for the metastasis

An adhering junction is a type of junction found in muscles that allow for rapid contraction and relaxation.

An adhering junction is a type of junction present in plant cells that help transport water and nutrients between cells.

An adhering junction is a junction formed by specialized proteins that regulate the cell cycle and cell division.

Adhering junctions are specifically involved in cell-cell adhesion and do not play a role in muscle contraction, plant cell transport, or cell cycle regulation.

Explanation

Adhering junctions are specifically involved in cell-cell adhesion and do not play a role in muscle contraction, plant cell transport, or cell cycle regulation.

6. What is the apical membrane?

Also called luminal or mucosal membrane and faces the lumen of an organ. Their properties are very variable (water permeability). It contains microvilli in highly reabsorptive or secretory epithelial cells. It DOES NOT contain the Na+/K+-ATPase (exclusion: choroid plexus)

The membrane responsible for binding hormones within the body.

A membrane found surrounding the entire outer boundary of an organ.

A membrane located at the base of an organ facing away from the lumen.

The apical membrane refers to the luminal or mucosal membrane that faces the lumen of an organ and has distinct characteristics.

Explanation

The apical membrane refers to the luminal or mucosal membrane that faces the lumen of an organ and has distinct characteristics.

7. What is the basolateral membrane?

It is a membrane that consists of basal membrane and lateral intercellular membrane, also called the serosal membrane. It faces the interstitial fluids. Properties are more similar between different basolateral membranes (high water and K+ permeability). It does not contain microvilli, but membrane infoldings. It expresses the Na+/K+-ATPase.

The basolateral membrane is specialized for absorption of nutrients and primarily expresses the Ca2+/Mg2+-ATPase.

The basolateral membrane is primarily composed of microvilli and is impermeable to water and K+.

The basolateral membrane faces the epithelial lumen and contains high levels of Na+ transporters.

The basolateral membrane is a critical component of epithelial cells and plays a key role in transport processes within the body.

Explanation

The basolateral membrane is a critical component of epithelial cells and plays a key role in transport processes within the body.

8. What does leaky epithelia mean?

Absence of epithelial cells in the organ

Less number of tight junctions
less selective
e.g. in the PCT in the kidneys

Highly selective characteristics in membranes

Presence of high number of tight junctions

Leaky epithelia refers to a condition where there are fewer tight junctions which results in less selectivity. This is commonly seen in the Proximal Convoluted Tubule (PCT) in the kidneys where substances can pass through more easily.

Explanation

Leaky epithelia refers to a condition where there are fewer tight junctions which results in less selectivity. This is commonly seen in the Proximal Convoluted Tubule (PCT) in the kidneys where substances can pass through more easily.

9. What does tight epithelia signify?

Medium number of tight junctions, moderately selective, the paracellular pathway allows some water passage.

Low number of tight junctions, not selective, the paracellular pathway is water permeable.

High number of tight junctions
Highly selective
e.g. in the CCD in kidneys
the paracellular pathway is water impermeable

Absence of tight junctions, highly selective, the paracellular pathway is water impermeable.

Tight epithelia are characterized by a high number of tight junctions, making them highly selective in terms of what can pass through them. Specifically, in the CCD in kidneys, the paracellular pathway is impermeable to water.

Explanation

Tight epithelia are characterized by a high number of tight junctions, making them highly selective in terms of what can pass through them. Specifically, in the CCD in kidneys, the paracellular pathway is impermeable to water.

10. Explain the difference in leaky and tight epithelia, in reference to solute absorption.

Paracellular Na+ and H20 absorption

Selectively permeable lipid absorption.

Apical and basal glucose absorption.

Transcellular K+ and Cl- absorption.

Leaky epithelia allow for paracellular Na+ and H20 absorption due to the presence of larger spaces between cells allowing ions and water to pass through, while tight epithelia prevent this type of absorption by having closer cell-to-cell junctions.

Explanation

Leaky epithelia allow for paracellular Na+ and H20 absorption due to the presence of larger spaces between cells allowing ions and water to pass through, while tight epithelia prevent this type of absorption by having closer cell-to-cell junctions.

11. What are the two types of epithelia and what do they do?

Defensive epithelia that protect the body from foreign invaders (e.g. skin, respiratory tract). Protection is achieved by the secretion of mucus and other defensive molecules.

Metabolic epithelia responsible for energy production and storage (e.g. liver, adipose tissue). This involves the breakdown of nutrients and synthesis of compounds like glucose and fatty acids.

Conductive epithelia involved in the transmission of electrical signals (e.g. neurons, cardiac muscle cells). Conductive epithelia use ion channels and pumps to generate action potentials for communication.

Absorptive epithelia (AE) is transport from mucosal(apical) to serosal(basolateral) solution (kidney, intestine). Absorption is driven by active Na+ transport. Leaky AE uses Na+ transport coupled with H+ transport, whereas tight AE uses Na+ apical membrane entry through ENaC. ENaC (Epithelial Na+ channel)

Secretory epithelia provides transport from the serosal (basolateral) to the mucosal (apical) solution. (slivary glands, pancreas, kidney). Here, secretion is driven by active Cl- transport.

Epithelia can be categorized based on their function as absorptive (transport from mucosal to serosal solution) or secretory (transport from serosal to mucosal solution). Epithelia with different functions have distinct characteristics and play vital roles in various physiological processes.

Explanation

Epithelia can be categorized based on their function as absorptive (transport from mucosal to serosal solution) or secretory (transport from serosal to mucosal solution). Epithelia with different functions have distinct characteristics and play vital roles in various physiological processes.

12. What epithelia does salivary glands have? Explain.

Look at slides

Stratified squamous epithelium

Simple cuboidal epithelium

Pseudostratified columnar epithelium

The correct answer advises to refer to slides for visual confirmation of the epithelia present in salivary glands, as it may vary based on the specific gland and species being studied.

Explanation

The correct answer advises to refer to slides for visual confirmation of the epithelia present in salivary glands, as it may vary based on the specific gland and species being studied.

13. What happens in hydraulic conductivity (water permeability)?

Water channels facilitate water movement and they are called: aquaporins. These AQP are expressed in the PCT and the Collecting duct, in the adrenal cortex. There is high water permeability in the PCT and tDLH (AQP1!!). There is almost no water permeability in the ascending limb, DCT and CNT. The only hormone that control water permeablility is in the collecting duct. Vasopressin induces incorporation of AQP 2 so the apical membrane has high water permeability.

The primary hormone controlling water permeability is adrenaline.

Aquaporins are mainly expressed in the ascending limb and Distal Convoluted Tubule (DCT).

Ascending limb has high water permeability due to a different type of aquaporins.

Hydraulic conductivity, also known as water permeability, is primarily facilitated by aquaporins expressed in different segments of the nephron. The correct hormone controlling water permeability is vasopressin, not adrenaline. Aquaporins are not mainly expressed in the ascending limb and DCT, their expression is prominent in the Proximal Convoluted Tubule (PCT) and the Collecting duct. Also, the ascending limb does not have high water permeability.

Explanation

Hydraulic conductivity, also known as water permeability, is primarily facilitated by aquaporins expressed in different segments of the nephron. The correct hormone controlling water permeability is vasopressin, not adrenaline. Aquaporins are not mainly expressed in the ascending limb and DCT, their expression is prominent in the Proximal Convoluted Tubule (PCT) and the Collecting duct. Also, the ascending limb does not have high water permeability.

14. Draw the cellular model of secretory epithelium.

Here-

Nowhere-

There-

Everywhere-

This question requires the examinee to demonstrate their understanding of the cellular model of secretory epithelium by drawing it accurately.

Explanation

This question requires the examinee to demonstrate their understanding of the cellular model of secretory epithelium by drawing it accurately.

15. What are the four factors that leaky and tight epithelia could be differentiated by?

-apical/basolateral transport proteins
-hydraulic conductivity (water permeability)
-responsiveness to hormones
-location within organs

- presence of cilia - size of the cells - number of cell layers

Leaky and tight epithelia can be differentiated by factors such as apical/basolateral transport proteins, hydraulic conductivity, responsiveness to hormones, and location within organs. Other factors like presence of cilia, size of the cells, and number of cell layers do not specifically define the difference between leaky and tight epithelia.

Explanation

Leaky and tight epithelia can be differentiated by factors such as apical/basolateral transport proteins, hydraulic conductivity, responsiveness to hormones, and location within organs. Other factors like presence of cilia, size of the cells, and number of cell layers do not specifically define the difference between leaky and tight epithelia.

16. Describe the localisation of leaky versus tight epithelia.

B. Leaky epithelia in the thin descending limb - Na+ reabsorption through active transport. Tight epithelia in the thick ascending limb through ANP receptors.

C. Leaky epithelia in the collecting duct - Na+ reabsorption through active transport. Tight epithelia in the loop of Henle through NHE3 transporters.

Leaky epithelia in the PCT - Na+ reabsorption thru solute and H+ coupling
Tight epithelia in CCT through ENaC

A. Leaky epithelia in the DCT - Na+ reabsorption through passive diffusion. Tight epithelia in the PCT through aquaporins.

Leaky epithelia are characterized by higher permeability and allow for greater movement of solutes whereas tight epithelia have lower permeability and restrict solute movement. The correct answer provided describes the localisation of leaky epithelia in the proximal convoluted tubule (PCT) allowing Na+ reabsorption through solute and H+ coupling, while tight epithelia are found in the cortical collecting tubule (CCT) and involve the epithelial sodium channels (ENaC). The incorrect answers do not accurately describe the localisation of leaky versus tight epithelia in the nephron.

Explanation

Leaky epithelia are characterized by higher permeability and allow for greater movement of solutes whereas tight epithelia have lower permeability and restrict solute movement. The correct answer provided describes the localisation of leaky epithelia in the proximal convoluted tubule (PCT) allowing Na+ reabsorption through solute and H+ coupling, while tight epithelia are found in the cortical collecting tubule (CCT) and involve the epithelial sodium channels (ENaC). The incorrect answers do not accurately describe the localisation of leaky versus tight epithelia in the nephron.

17. Summarise leaky versus tight epithelia.

Leaky epithelia primarily rely on Na+/H+ exchanger for Na+ re-absorption, while tight epithelia utilize Na+/Cl- co-transporter for the same purpose.

Leaky epithelia (e.g. renal prox. tubule)
-Na+-coupled solute transport, Na+/H+ exchanger
-high rates of Na+ re-absorption
-high hydraulic conductivity (para-cellular, aquaporins) tight epithelia (e.g. renal cortical collecting duct)
-Na+/Cl- co-transporter and Na+-channel (ENaC)
- low rates of Na+ re-absorption
-low hydraulic conductivity (only via aquaporins, AQP2)

Leaky epithelia have low hydraulic conductivity and utilize Na+/Cl- co-transporter, while tight epithelia exhibit high hydraulic conductivity with Na+/H+ exchanger.

Leaky epithelia exhibit low rates of Na+ re-absorption with low hydraulic conductivity, while tight epithelia have high rates of Na+ re-absorption through Na+/H+ exchanger.

Leaky epithelia are characterized by high rates of Na+ re-absorption and high hydraulic conductivity, while tight epithelia exhibit low rates of Na+ re-absorption and low hydraulic conductivity. This distinction is due to the different mechanisms of solute transport and channels present in each type of epithelium.

Explanation

Leaky epithelia are characterized by high rates of Na+ re-absorption and high hydraulic conductivity, while tight epithelia exhibit low rates of Na+ re-absorption and low hydraulic conductivity. This distinction is due to the different mechanisms of solute transport and channels present in each type of epithelium.