Important concepts in biology

Important concepts in biology PCAT Review Course Day II Maggie McCormick (memccorm@med.unc.edu) Tricia Lenhart (patricia_lenhart@med.unc.edu)

Outline for today • Muscles and Locomotion • Vertebrate skeleton • Muscle system • Digestion • Digestion in humans • Excretion • Kidney structure • Kidney function • Respiration in Humans • Gas exchange • The lungs V. Endocrinology • Negative feedback loops • Hormones • Adrenal gland • Pituitary gland • Thyroid • Parathyroid • Pineal gland VI. Plant Biology • Cellular structure • Photosynthesis • Dark reactions • Vascular system • Reproduction

Vertebrate skeletal system Osteoblasts – Build bone Osteoclasts – Clear bone (break it down) Chrondytes – Synthesize cartilage

Striated Skeletal Muscle

Structure of the Sarcomere During a muscle contraction, the H zone and I band shorten, but the A band does not

Neuromuscular junction and contraction stimulation

Recruit more muscle fibers Activate more motor units to increase the strength of contraction Summation Increase the frequency of stimulation to get an additive effect A single muscle fiber has a limit on how far it can contract. How do we get stronger and weaker contractions from a muscle?

No sarcomeres – not striated! One nucleus per cell Involuntary contraction – innervated by the autonomic nervous system Found in the digestive tract, bladder, uterus, and blood vessel walls Has sarcomeres – striated One or two nuclei per cell Involuntary contraction – controlled by pacemaker cells and the autonomic nervous system Cardiac Muscle Smooth Muscle

Oral cavity Mastication for mechanical breakdown Saliva acts as solvent Salivary enzymes (amylase) begin to break down starch Digestion

Esophagus • Pushes food down to stomach by peristalsis (waves of involuntary muscle contraction) Gastroesophageal Reflux Disease (GERD)

Stomach • Lined with mucus to protect against acid and enzymes • Churns food into a mixture called chyme • Gastric glands secrete: • HCl – Antibacterial, solubilizes food, activates enzymes • Intrinsic factor – B12 absorption • Pepsinogen – converted to pepsin, a protease

Enzymatic Breakdown of chyme Lipases Aminopeptidases Disaccharidases Lactase Small Intestine

Small Intestine Absorption of nutrients through specialized structures called villi

Large Intestine Absorbs water and salt Home to bacterial colonies that break down undigested food and synthesize vitamins Retained osmolytes can lead to diarrhea Liver Secretes bile into the gall bladder for storage Bile emulsifies fat and allows absorption across the plasma membrane Pancreas Secretes digestive enzymes Secretes bicarbonate Synthesizes insulin for blood glucose control

Digestive Enzymes

The Kidney - Excretion

The Nephron: the functional unit of the kidney

Urine formation • Three steps to formation of concentrated urine: • Filtration • Secretion • Reabsorption

Filtration in the Bowman’s Capsule “Filtrate” Filtered: water, small cations (Na+,K+, H+), anions (Cl-, HCO3-) , glucose, amino acids, urea, and anything small with a positive/neutral charge. Excluded: blood cells, proteins over a certain size (such as albumin), and negatively charged things (like most small proteins)

Secretion and Reabsorption Proximal Tubule: Primary site of nutrient and water reabsorption

Secretion and Reabsorption • Loop of Henle: • Regulates water, sodium, and potassium loss in the nephron • Sets up osmolarity gradient through the counter-current-multiplier system

Secretion and Reabsorption Distal Tubule: Primary site for secretion of substances into the filtrate

Secretion and Reabsorption • Collecting Duct: • Primary site for regulating water reabsorption • Permeability is effected by the hormone ADH/vasopressin

Regulation of blood pH Body fluid pH = 7.4 Lungs remove CO2, kidneys remove H+ Acid-Base disorders and compensatory mechanisms Two types of disorders: Respiratory – affect blood acidity by causing changes in PCO2. Metabolic – affect blood acidity by causing changes in HCO3-.

Respiration: The Lungs External Nares Nasal Cavity Pharynx Epiglottis Larynx Be able to remember the path of air from the nose to the alveoli

Respiration: Gas Exchange From Right Ventricle • Alveoli maximize surface area to increase the efficiency of gas exchange. • Total surface area is roughly the size of a tennis court! To Left Ventricle

Breathing rate control The medulla oblongata detects blood pH levels (more acidic means more C02) Carotid and Aortic chemoreceptors detect blood O2 and CO2 levels But CO2 levels are always the priority unless you’re suffocating! The medulla oblongata stimulates the diaphragm

Endocrine System: Glands and Hormones • Glands secrete hormones into the circulatory system • Hormones are the body’s messengers, coordinating the activities of different organ systems • Each gland may produce many different hormones, each with different targets and effects • See the handout for a list of the most important hormones produced by each gland! Pineal

Two major hormone groups: Peptides • Proteins of varying size and complexity • Bind to receptors on target-cell surface • Often generates cyclic AMP (cAMP) as a second messenger • The cascade of signaling events amplifies the hormone’s effect in the cell Steroids • Lipid-solublering structure • Cross the target-cell membranes and bind to cytoplasmic receptors • Hormone-receptor complex enters the nucleus and directly induces gene expression Testosterone

Examples of important hormones… • Adrenal Medulla  Epinephrine (adrenaline) • Releases glucose from the liver and muscles, increases metabolic rate, increases strength and rate of heartbeat, dilates and constricts blood vessels to deliver more blood to the muscles, heart, and brain. The “fight or flight” response triggered by the sympathetic nervous system! • Anterior Pituitary  Prolactin • Stimulates milk production in mammary glands • Pancreas  Insulin • Released in response to high blood glucose. Stimulates uptake of glucose by muscles and adipose tissue (fat) and storage of glucose as glycogen in the liver and muscles. Underproduction or insensitivity to insulin leads to diabetes, the most common endocrine disorder!

Feedback loops keep hormone levels balanced

Plant Biology: Cellular Structure • Plant Cells Do NOT have: • Centrosomes • Lysosomes

Photosynthesis is split into Light and Dark Reactions • 6CO2 +12H2O + light energy C6H12O6 (Glucose) + 6O2 + 6H2O

Light Reactions

Dark Reactions (Calvin Cycle) In: 3 CO2, 9 ATP, 6 NADPH Out: Glyceraldehyde-3-Phosphate, 9 ADP, 6 NADP NOTE: This is the opposite of the Krebs cycle! (Instead of breaking down a 3-carbon molecule into CO2 to make ATPs and NADHs, we take 3 CO2s and make a 3-carbon molecule; a process that burns up ATPs and NADHs!) Phosphoglyceraldehyde (PGAL)

Plant Biology: Vascular System The phloem transports water and food in both directions The xylem transports only water, up from the roots

Plant Biology: Sexual Reproduction

Review questions • Put the following in proper order: - larynx, bronchi, trachea, pharynx • Does the medulla oblongata detect blood CO2, O2, or pH? • Give an example of a hormone produced by the adrenal medulla and it’s effect on the body. • Where do the light reactions of photosynthesis take place? • What is the important product of the Calvin Cycle?

Important concepts in biology