BS 1: Membranes, Transport, Homeostasis & Tissues

For a 30 year old 70 Kg male (avg male), what is the composition of fat, lean body mass and water?

• 18% fat

• 22% lean body mass

• 60% water

What is the split of numbers (in L) for total body water (TBW)?

1. Total body water (TBW) = 42L

   • TBW → intracellular fluid (ICF) = 25L

   • TBW → extracellular fluid (ECF) = 17L

What is the split of numbers for extracellular fluid (ECF) and for what fluids?

• ECF → Interstitial fluid (ISF), plasma & Transcellular fluid

  • ISF = 13L

  • Plasma = 3L

  • Transcellular fluid = 1L

What is the definition of Transcellular fluid?

Any fluid that has crossed over an epithelial membrane

What are 6 examples of transcellular fluids?

1. Cerebrospinal fluid (brain)

2. urine (kidney & bladder)

3. gastrointestinal secretions (saliva, gastric juice, pancreatic juices, bile)

4. sweat

5. aqueous and vitreous humours (eye)

6. synovial fluids (joints)

True or False: the ionic composition between intracellular & extracellular fluid is the same.

FALSE u silly betch

the compositions are very different

intra has a lot less Cl- and Na+, and more K+ & protein

True or False: the osmolality in all fluid components other than transcellular is the same at 290mOsm, when at rest.

TRUEEEEE

True or False: the balance of ions in the interstitial fluid and blood plasma is very similar.

TRUEEEEE

they’re both extracellular fluids

Is there any protein in the blood plasma? if so how many mM?

Yes there is

1mM

Is there any protein in the interstitial fluid? if so how many mM?

#no

What is the main positive ion and main negative ion in the extracellular fluid?

• main +ive ion = Na+

• main -ive ion = Cl-

What is the main positive ion and main negative ion in the intracellular fluid?

• main +ive ion = K+

• main -ive ion = Cl-

but much less Cl- in intracellular, down to 20 mM from approx. 110 in extra.

Is there more or less protein in the intracellular fluid than the extracellular? by how much?

• more protein

• 4mM(ICF) vs 1mM(ECF)

What is the barrier between the ICF and ISF?

Plasma membrane/cell surface membrane

What is the barrier between the ISF and transcellular fluid

Epithelium

What is the barrier between the ISF and plasma

endothelium

What are 3 features of the plasma membrane?

• its phospholipid bilayer has high selective permeability e.g., impermeable to water based molecules

• lots of transport proteins for uptakes and removal of specific solutes

• vital for regulation of the intracellular environment

What is the phospholipid bilayer impermeable to?

what increases permeability of the membrane?

• impermeable to ions and polar molecules

• transporters/membrane proteins

How many different types of membrane proteins/transporters?

What are they?

3 types

• Channels

• carriers

• pumps

What are the 2 categories of transporter?

1. Passive transport - driven by gradients e.g., Channels, carriers

2. active transport - ATP hydrolysis e.g., pumps

What are the 3 types of carriers? what does each one do?

1. Uniport/facilitator - moves one type of ion in one direction

2. Symport/co-transporter - moves two ions in the same direction, often opposite charges

3. Antiport/exchanger - takes one ion out and a dif ion in, usually of the same charge (+1/-1) to maintain electrical neutrality

what are 2 functions of transport proteins?

1. uptake of nutrients, substrates, cofactors, and export of waste products

2. regulation of intracellular ions (gradient maintenance), pH (acid & Base extrusion), cell volume (to prevent bursting, regulatory volume increase and decrease as water follows behind ion movement)

What generates a membrane potential?

what is the membrane potential at rest? (in mV)

the asymmetric distribution of K+ i.e., 120mM ICF vs 5mM ECF

this maintains an electrochemical conc gradient at approx -70 mV

What is water distribution across a cell determine by?

by OSMOSIS

water moves through aquaporins/passively following ions

at rest osmolality is the same, because water distributes itself so that the osmotic pressures are equal

What are 3 features of the capillary endothelium?

1. v. thin layer of cells lining blood vessels

2. highly permeable (leaky) in some organs (e.g., kidneys) and not others (e.g., brain)

3. important role in regulation of the interstitial fluid

What is water distribution across a capillary endothelium determined by?

• hydrostatic pressure

• colloid osmotic pressure (osmolality)

What are 3 features of the epithelia?

1. layers of cells covering internal and external surfaces of organs and tissues

2. has a protective/barrier function

3. important roles in absorption and secretion

what are 3 parts of the epithelial cell to remember?

1. apical membrane

2. basolateral membrane

3. tight junction

What are other names for the external and internal environment?

peripheral and core

What kind of fluctuations do you get in the external/peripheral environ?

large fluctuations in;

• temp

• diet

• availabilty of water etc

What kind of fluctuations do you get in the internal/core environ?

small fluctuations in:

• temp

• pH [O2] [CO2]

• [glucose]

• blood pressure

What is the definition of Homeostasis?

maintenance of a constant environ in response to internal or external factors

What is negative feedback control?

Regulation of a system to maintain a controlled variable at its set point

set point - value/threshold that a variable should be maintained at to be healthy

it is a self-monitoring system

what are the basic steps of negative feedback?

1. change in variable

2. detection by receptor/sensor

3. sent to integrating centre (afferent pathway)

4. sent to effector system brings about correction of the variable (efferent pathway)

5. correction of variable detected at integrating centre so effector system stops

6. hence self-monitoring system

What are the steps for regulation of blood pressure via a negative feedback control system?

1. fall in blood pressure

2. baroreceptors (stretch sensitive in carotid arteries & aortic arch) detect change

3. sent via glossopharyngeal nerve to medulla oblongata (has control over cardiac system)

4. sent via autonomic nerves to the heart blood vessels

5. these increase cardiac output and vasoconstriction to return blood pressure to normal

What is a diurnal change in set point?

change in a set point over 24hr cycle

give an example of a diurnal change

e.g., body temp

• body temp drops when sleeping

• because not expending much energy relatively still

• but when awake = moving, eating, metabolism speeds up

• therefore temp increases, aiding in enzymes and kinetics

What is positive feedback control? give examples.

when the initial stimulus causes a response which reinforces itself

e.g., action potentials in nerves, ovulation, blood clotting

what are the 2 control systems?

1. nervous system

   • rapid (seconds)

   • short term effects

2. endocrine

   • slower (minutes to days)

   • long term effects

What are the divisions of the nervous system?

1. Nervous system

   • Central (CNS)

   • Peripheral (PNS)

2. CNS

   • Brain

   • Spinal Cord

3. PNS

   • autonomic nerves (involuntary)

     • parasympathetic - rest and digest

     • sympathetic - fight or flight

     • e.g., smooth & cardiac muscle, glands

   • somatic nerves (conscious control)

     • e.g., skeletal muscle

What is the basic pathway that the autonomic nerves take to the target cells?

preganglionic neuron (CNS) → postganglionic neuron (PNS) → target cell

List 5 comparisons of the sympathetic and parasympathetic systems

	Sympathetic	Parasympathetic
Outflow from CNS	thoracic & lumbar parts of spinal cord	cranial & sacral part of spinal cord
Preganglionic fibre length	short	long
ganglionic transmitter	ACh (N2)	ACh (N2)
ganglionic receptor	N2 receptor	N2 receptor
postganglionic fibre length	long	short
neuroeffector transmitter	Noradrenaline/norepinephrin (α or β)	ACh (M)
postganglionic receptor	α and β adrenergic receptors	M - Muscarinic ACh receptor
Effector tissues	smooth muscle, cardiaac muscle, gland	smooth muscle, cardiaac muscle, gland

what are functional roles of the peripheral nervous system?

• Both divisions innervate most organs and tissues

• Often have opposing (antagonistic) effects

• Sympathetic more active in stressful situations (‘flight or fight’ response)

• Parasympathetic more active in vegetative situations (lectures…)

What flow of steps happen in the adrenal medulla for release of epinephrine/adrenaline?

1. sympathetic neuron from CNS synapses in adrenal medulla

2. releases ACh(N2)

3. binds to N2 receptor on a chromaffin cell

4. epinephrine secreted into circulation

Give examples of +ive & -ive feedback systems under hormonal control

1. -ive feedback = release of cortisol

   • Corticotrophin releasing hormone (CRH) released by hypothalamus

   • this stimulates release of adrenocorticotrophic hormone (ACTH) from pituitary gland

   • this stimulates high levels of cortisol release from liver

2. +ive feedback system = lactation

   • suckling on mammary gland

   • oxytocin released from posterior pituitary gland

   • milk released

   • loop broken when baby stops suckling (external break of loop)

What is the organisation of the body from smallest to largest?

• cell - Fundamental structural and functional unit of the body

• Tissue - A collection of cells that perform a particular function

• Organ - Multiple tissues that perform a particular function by working together

• System - A group of organs with a collective function

• Organism - One complete individual

What are the 4 basic tissues?

1. Epithelia

2. Connective tissue

3. Muscle

4. Nervous

What is the definition of histology?

What does histology allow us to do?

The study of anatomy at the cellular level (and therefore tissues)

Knowing the histology of a structure allows you to work out its function

What are 3 places that epithelia can be found (generally)

1. Cover surfaces e.g., skin

2. lining cavities and tubes e.g., blood vessels

3. forming glands e.g., sweat & sebaceous glands

What are the 4 important characteristics of epithelia?

1. Attachment - cells adhere to each other, a basement membrane and nearby structures, this maintains integrity of the epithelial barrier

2. Avascularity - no blood supply, nutrients from other sources

3. Regeneration - epithelia are found in layers, cells underneath replace those above, e.g., skin

4. Polarity (apical & basal) - have top and bottom end

What is the basic structure of epithelial cells?

closely packed cells supported by a basement membrane/basal lamina

most epithelial linings are also supported by connective or another type of tissue

What are the 2 things that classification of epithelia is based on?

based on the number of cell layers & shape of cells

but in the most superficial (outermost) layer

What are the different number of cell layers, and the different shapes of epithelium called?

Number of cell layers:

• simple - one layer

• stratified - two or more layers

Shape:

• squamous (flat, oval shaped nucleus)

• cuboidal (cube, round shaped nucleus)

• columnar (rectangular, oval-shaped, basally located nucleus)

What is the major function and common locations of simple squamous epithelium?

major function: exchange of nutrients and gases

location: blood vessels, alveoli

What is the major function and common location of non-keratinised stratified squamous epithelium?

major function: protection, barrier

location: oral cavity, oesophagus

i.e., found in places where the body is undergoing mechanical stress

What is the major function and common location of keratinised stratified squamous epithelium?

associated with keratin

major function: protection, waterproof barrier

location: skin

What is the major function and common location of simple cuboidal epithelium?

basally located nuclei

major function: absorption & secretion, often with surface modifications e.g., microvilli to increase SA

location: gastrointestinal tract

What is the major function and common location of pseudostratified ciliated columnar epithelium with goblet cells?

why is it called pseudostratified?

modifications: cilia & goblet cells

major function: mucociliatory escalator - mucus traps debris and cilia wafts it away

location: trachea and large respiratory airways

pesudostratified because appears to be stratified, as some cells don’t reach free surface, but actually all cells touch basement membrane

What are the 4 types of intercellular junctions?

1. Desmosomes

2. Hemidesmosomes

3. Tight Junctions

4. Gap Junctions

What is a desmosome? What is its function?

Very strong connections that join adjacent cells that resist stretching and twisting

What is a hemidesmosome? What is its function?

Attach cells to the basement membrane thereby stabilising the position of the cell and anchoring the basal end of the cell to the underlying tissue

What are tight junctions? What is its function?

• Located near the apical side of the cells

• Adjacent cell membranes bound together by interlocking proteins

• Prevents passage of water and solutes between cells

  e.g. in digestive tract prevent digestive fluids passing between epithelial cells

What are gap junctions? What is its function?

• Interlocking membrane proteins (connexons) hold cells together

• Connexons contain a central pore which allows movement of small molecules and ions between cells

• Found in cardiac muscle

What are 6 functions of connective tissue?

1. Forms a structural framework for the body

2. Supports, surrounds and interconnects other tissue types e.g., abdominal cavity

3. Protects delicate organs

4. Transports fluids and dissolved materials

5. Stores energy reserves e.g., many connective tissues have adipose cells where energy reserves come from

6. Defends body from microorganisms e.g., lymphocytes within tissue

What does connective tissue consist of?

What are the 2 classifications of connective tissue?

Consists of cells within an extracellular matrix

1. specialised connective tissue

2. connective tissue proper

What type of cells are in the connective tissue?

• fibroblasts; main cell type that synthesises the extracellular matrix

other cell types:

• adipocytes

• macrophages

• mast cells

What are the 3 tissues fall under the specialised connective tissue classification and why?

1. Blood - watery EcM

2. Bone - tough EcM

3. Cartilage - jelly like EcM

they are all still connective tissues because they have an extracellular matrix (EcM), but just with different consistency

What 5 factors is the connective tissue proper classified by?

• type

• arrangement of fibres

• abundance of fibres

• cell types

• ground substance

What are features of the loose areolar connective tissue? Where is this found?

Contains:

• lots of ground substance

• few fibres (collagen & elastic)

• variety of cells

  • Fibroblasts

  • Adipocytes

  • Macrophages (transient)

Found under the epithelium that covers and lines the body surfaces

What are features of the dense irregular connective tissue? Where is this found?

Contains:

• little ground substance

• many collagen fibre bundles arranged haphazardly

• few cells (mainly fibroblasts)

resists excessive stretching and distension

found in the dermis

What are features of the dense regular connective tissue? Where is this found?

Contains:

• little ground substance

• many densely packed bundles of collagen fibres arranged in parallel rows 

• few cells (mainly fibroblasts)

found in tendons and ligaments

What is the function of muscle tissue?

Produces movement and is specialised for contraction

What are the types of muscle tissue?

1. Skeletal

2. Smooth

3. Cardiac

What are 3 similarities between all type of muscle?

1. Elongated parallel to axis of contraction

2. Numerous mitochondria

3. Contractile elements

What are the functions and features of skeletal muscle?

• Moves and stabilises the skeleton

• Forms sphincters in digestive and urinary tracts

• Involved in respiration

• Long, cylindrical cells

• Striated (striped dark & light bands)

• Multinucleated

• Innervated by somatic nervous system

What are the functions and features of smooth muscle?

• Located in the walls of organs, blood vessels and airways

• Gastrointestinal movement

• Alters diameter of airways and blood vessels

• Short, fusiform cells

• Non-striated

• Single, centrally located nucleus

• Innervated by autonomic nervous system

What are the functions and features of cardiac muscle?

•  Found in the heart wall

•  Helps to circulate blood & to maintain blood pressure

• Branched muscle fibres

• Striated (dark & light bands)

• 1-2 central nuclei

• Intercalated discs

• Innervated by the autonomic nervous system