Lecture 3: Cells and Tissues

Bio 219Dr. Adam Ross

Cell Physiology

Cell Physiology

• Brief review of organelles• Should be mostly review

• Cell surrounded by plasma membrane• Lipid bilayer• Also surrounds organelles• Polar heads face aqueous environments• Non-polar tails face inwards away from polar aqueous environment

Nucleus

• Site where DNA is stored• Transcription happens here• DNA to mRNA

• Gene expression can be regulated by a number of factors• Contains nucleolus

Rough Endoplasmic Reticulum

• Associated with the ribosome• Non membrane bound organelle (ribosome)• Makes proteins from mRNA

• Also folds proteins

Ribosome

• Protein machinery responsible for translating mRNA into polypeptides• See Previous Lecture

Smooth E.R.

• Synthesizes lipids, phospholipids, and steroids• Carbohydrate metabolism• Detoxification of drugs• Gluconeogenesis

Mitochondria

• Produces ATP• H+ ion gradient drives ATP-synthase• Created by electron transport chain

Cell Membrane

• Lipid bilayer also contains other non-phospholipid elements• Cholesterol• Glycoproteins• Receptor proteins• Surface proteins• Glycolipids

Plasma Membrane

Cytoplasm

Extracellularfluid

Carbohydrate

Cholesterol

Surfaceprotein

Filaments ofcytoskeleton

Embeddedprotein

Plasma membrane

Outer surface of plasma membrane

Inner surface of plasma membrane

Plasma membrane

Phospholipidbilayer

Glycoprotein

Glycolipid

Three basic ways to transport things

• Pores• Non gated channels. Always open

• Channels• Gated pores, allow transport when open

• Carriers• Opens upon presentation of thing to be transported• Generally unidirectional

Pores, channels and carriers

• Pores- always open• Aquaporin channels in kidney• Look like a straight, open tube

• Channels• Alternatively open and closed• Allow specific things to pass• Ion channels regulate cell membrane potential

• Carriers• Two gates that are never open at same time• Never provides continuous path

Membrane proteins have diverse functions• Ionotropic receptor (type of gated channel)• Nicotinic acetylcholine receptor (nAChR)

• Voltage gated channel• Opens in response to changes in electrical potential

• Metabotropic receptor• β-adrenergic

• Transport proteins• Na-K ATPase

• Structural Proteins• Integrin

Ionotropic receptors

• Binding of ligand to receptor opens ion channel• Allows ions to enter or leave cell, changing the electrical potential or activity

of a cell or downstream messenger

• nAChR• In skeletal muscle; allows for communication between nerves and muscles• Binding of acetylcholine to nAChR, opens a cation channel which starts the

process of muscle contraction

• There are also voltage gated ion channels• Open in response to changes in cell electrical potential

nAChR

Metabotropic receptors

• Binding of ligand causes metabolic cascade of G-proteins• This cascade used second messengers to change activity of some cellular

parameter• In the heart muscarinic acetylcholine receptors are used to slow heart rate

• Use of heterotrimeric G-protein

Metabotropic vs ionotropic

Transport proteins

• Transport can be active or passive• Example: Glucose transporters (GLUT)

Cotransporters

• Can also be called exchangers• Exchange one molecule or ion for another• Generally driven by the inward Na+ gradient

• Many examples• Na/Glucose• K/Cl

Connective proteins

• Surface proteins that aid in cell to cell adhesion• Integrin is one example

• Interacts with extracellular matrix to help provide cell stability

• Tight junctions• Make gaps between cells impenetrable• Made up of a number of proteins

• Gap junctions• Allow for electrical communication between cells

• Via direct cell to cell exchange of ions and/ or small molecules• Found in most cells in solid tissue

Integrin

Tight junctions

Gap junctions

Membrane has a diverse array of functions• Protect cell from pathogens• Maintain proper salt-water balance• And corresponding membrane potential

• Respond to signaling ligands via surface receptors• Endo and Exocytosis• Anchor cell in place• Communication with neighboring cells

4 basic tissue types

• Epithelial• Connective• Neuronal• Muscular

Epithelial tissue

• Continuous sheets of cells• Squamous, columnar, cuboidal

• Boundary covering internal environment (ECF) from external environment• Covering/ lining epithelia• Protection/ absorption

• Skin• GI tract

• Secretory epithelia• Exocrine and endocrine glands

Types of epithelial tissue

• Squamous• Flattened sheet of cells

• Columnar• Tall column shaped cells

• Cubodial• Cube shaped cells

• Simple• Single layer of epithelial cells

• Compound/ Stratified• Multiple layers of cells

Squamous epithelia

• Simple• Single layer• Often a mediator of filtration and diffusion

• Stratified• Multiple layers• Only one layer of cells is attached to the basement membrane• Good for areas with lots of abrasion

Squamous epithelia

Simple: Glomerulus on top, Bowman’s capsule on bottom

Stratified: Human epidermis

Columnar epithelia

• Simple• Single layer of column shaped cells

• Most organs of human digestive tract

• Stratified• Secretion and protection

• Urethra, vas deferens, uterus, eye, anus

• Pseudostratified• Appears to be stratified

• Actually only one layer of cells• Linings of upper respiratory tract (ciliated)• Male vas deferens (non-ciliated)

• Ciliated• Columnar cells have cilia attached to the apical membrane

• Used to trap debris

Columnar epithelia

Simple (stomach)

Cubodial epithelia

• Simple• Single layer of cube shaped cells

• Kidney tubules, glandular ducts

• Stratified• Sweat, mammary, and salivary glands

• Often times only top layer is cuboidal, other layers are other cell types

Cubodial epithelia

Parotid gland (stratified)Pig kidney

Functions of epithelial

• Exchange• Simple squamous; alveoli

• Transport• Simple columnar; small intestine & simple cuboidal; renal tubule

• Ciliated• Pseudostratified; trachea & simple ciliated columnar; uterine tube

• Protective• Stratified squamous; skin

• Secretory• Glandular; endocrine and exocrine glands

Connective tissue

• Major support tissues of the body• Most abundant and diverse tissue type• Storage site for fat• Composed of cells and extracellular matrix• Considered to be two parts of one thing

• Cells are tissue specific• ECM is mostly protein fibers used for anchoring and support

Types of connective tissue

• Many different types of connective tissue:

1. Areolar2. Adipose3. Dense (Tendons and Ligaments)4. Cartilage5. Bone6. Blood

Loose connective tissue (Fibroblasts)

Loose adipose tissue

Adipose (fat) tissue• Found under skin, around kidneys and heart• Functions in energy storage and insulation; cushioning for organs

Dense connective tissue

Dense connective tissue• Found in tendons and ligaments• Forms strong bands that attach bone to muscle or bone to bone

Cartilage

Cells = chondrocytes

Bone

Bone- functions

• Functions:1. Protects and supports internal structures2. Facilitates movement along with muscles3. Stores lipids, calcium, and phosphorus4. Produces blood cells

Bone

Bone• Found in the skeleton• Functions in support, protection (by enclosing organs), and movement

Blood

Blood• Found within blood vessels• Transports nutrients, gases, hormones, wastes; fights infections

Blood

• Blood consists of liquid (plasma) and formed elements including:• Red Blood Cells (RBC) - transports oxygen to body cells.

•White Blood Cells (WBC) - fight infection

• Platelets—cell fragments necessary for clotting of the blood.

Connective tissues

Neuronal tissue

• Designed to transmit information from one part of the body to another• Uses electrochemical signals• Action potentials• Neurotransmitters

• Synapses

• Also includes support cells for the cells sending the messages (neurons)• Microglia, astrocytes, schwann cells, etc

Nervous tissue

Figure 4.4

Dendrite

Cell body

Axon

Neuron

Neuroglia

Muscular tissue• Cardiac, skeletal, and smooth muscle in the body• Produces force to move body, pump blood, or help move digested

food.• Relies on the interaction of actin and myosin to produce force• Different muscle tissues have different properties• Will cover in depth during muscle lecture

Skeletal muscle

• Voluntary• Striated• Activated by acetylcholine release at synapse• Majority of body’s energy and blood are used here

Skeletal muscle

Cardiac muscle

• Only in the heart (duh.)• Involuntary• Striated• No direct neural control

Smooth muscle

• Involuntary• Non striated• Involved in digestive process