Human Physiology - Lecture Exam 2

BIOSC-140 Lecture Examination 2 : Cellular Metabolism, Communication and Homeostasis, and the Nervous System

What is “Bioenergetics”?

The study of energy flow through biological (living) systems.

How do chemical reactions work as a means of energy transfer?

Molecular bonds are energy relationships. The process of making/breaking bonds function as a means of energy transfer.

What are “substrates”?

Molecules at the beginning of a chemical reaction. Also known as “reactants”.

What are “products”?

Molecules at the end of a chemical reaction.

How do we get a metabolic pathway?

By coupling reactions in a series.

What is an example of a metabolic pathway?

Glycolysis.

What is the substrate and end product of glycolysis?

Substrate = Glucose

End Product = Pyruvic Acid (x2)

What are “intermediates”?

The substances made in the middle of a metabolic pathway.

What is a metabolic pathway?

A series of reactions that transfer energy from one molecule to another.

What do weak acids ionize to yield?

a hydrogen ion plus an anion

What is an example of a weak acid?

lactic acid

What suffix is utilized for weak acids?

-ic acid

What is the notable attribute of weak acids?

Weak acids dissociate at normal physiologic pH.

What happens when a weak acid undergoes conversion?

They lose their hydrogen ion and become an anion. The result is a strong acid.

What is an example of a strong acid?

lactate

What percentage of lactic acid becomes lactate?

well over 99%

What is free energy?

Potential energy stored in chemical bonds that is able to do work.

Where is all of the free energy in humans stored?

Within chemical bonds.

What holds higher free energies?

Complex molecules have more chemical bonds and therefore higher free energies. An example of this is Glycogen.

What are catabolic pathways?

Metabolic processes that break down complex molecules into simpler ones in order to liberate energy.

What does anaerobic metabolism break down?

only carbohydrates

What does aerobic metabolism primarily break down?

carbohydrates and lipids (and sometimes protein)

Does anaerobic metabolism result in large or small energy yield (ATP)?

relatively small energy yield

Does aerobic metabolism result in large or small energy yield (ATP)?

large energy yield

Does anaerobic metabolism utilize oxygen?

no

Does aerobic metabolism utilize oxygen?

yes

What is the general metabolic pathway for anaerobic metabolism?

glucose → pyruvate → lactate → few ATP

What are the general metabolic pathways for aerobic metabolism?

1. glucose → pyruvate → Kreb’s cycle → electron transport system → ATP

2. triglyceride → Kreb’s cycle → electron transport system → ATP

What is glycolysis?

The main catabolic pathway found in the cytoplasm. The conversion of glucose into pyruvate.

Where does glycolysis occur?

Outside the mitochondria (specifically within the cytosol).

Does glycolysis require oxygen?

no, but more energy is produced if oxygen is available and the mitochondria are used

What are the end products of glycolysis?

• 2 pyruvate

• 2 ATP (4 ATP are produced, but two are used in the process)

• 2 NADH

What are the two possible fates of one produced pyruvate within humans?

1. Anaerobic (stays in cytosol), it becomes pyruvate

2. Aerobic (enters mitochondria), turns into acetyl CoA which then goes through Kreb’s cycle to make ATP

What is glycogenolysis?

The breaking of glycogen into glucose.

What is glycogenesis?

The making of glycogen from glucose.

What is gluconeogenesis?

Making glucose from nonglucose precursors such as lactic acid and protein.

What is lipolysis?

The breaking apart of lipids, especially refers to triglycerides.

What is lipogenesis?

The making of lipids, especially refers to triglycerides.

What is proteogenesis?

The making of proteins (but usually called protein synthesis).

What is proteolysis?

The breaking down of proteins.

What does “ATP Used” refer to?

The number of ATP that has to be broken down for energy in order to get the pathway started.

What does “ATP Direct” refer to?

What is made through substrate level phosphorylation where ATP is directly produced within the metabolic pathway.

What does “ATP Indirect” refer to?

Oxidative phosphorylation where ATP is produced from NADH or FADH₂ through the electron transport chain.

What does “ATP Total” refer to?

The total amount of ATP that is produced for a specific cycle. It’s obtained by adding the ATP Direct and the ATP Indirect.

What does “ATP Net” refer to?

The difference between the total ATP and the used ATP. It’s calculated by subtracting the used ATP from the total ATP.

What is the ATP yield for the oxidation of one molecule of NADH?

3 ATP

What is the ATP yield for the oxidation of one molecule of FADH₂?

2 ATP

What is the overall electron chain transport reaction?

2 H⁺ + 2 e^- + ½ O₂ → H₂O + energy

Where is the electron transport chain located?

Within the mitochondria.

What are the steps for the aerobic metabolism of lipids?

1. lipolysis

2. beta oxidation

3. kreb’s cycle

4. electron transport chain

What are the steps for the aerobic metabolism of proteins?

1. proteolysis

2. gluconeogenesis (glycolysis first), ketogenesis (kreb’s cycle first)

3. glycolysis and activation of pyruvate

4. Kreb’s cycle

5. electron transport chain

What is direct cytoplasmic transfer?

The transferral of chemical or electrical signals directly from one cell to an adjacent cell (i.e. gap junctions)

What are the three local chemicals that facilitate cell to cell communication?

1. Autocrines

2. Paracrines

3. Neurotransmitters

What do autocrine chemicals act on?

themselves

What do paracrine chemicals act on?

neighboring cells

What do neurotransmitters act on?

synapses and diffuse to receptors

What are the two ways that cells communicate over long distances?

1. neural

2. humoral

How do neural pathways aid in cell to cell communication?

neurons transmit electrical signals down axons

How do humoral changes aid in cell to cell communication?

hormones travel in the blood to distant target cells that have receptors

What are signal pathways?

pathways in which cells signal or communicate with other cells

What are the energy sources utilized by cells?

1. ATP

2. Creatine Phosphate

3. Anaerobic Metabolism

4. Aerobic Metabolism

What processes does the endocrine system control?

• extrinsic regulators that maintain homeostasis

• growth and development

• metabolism

• temperature

• hunger

• thirst

• emotions

• immune system

• digestion

• blood volume and composition

• smooth and cardiac muscle regulation

• reproduction

What are the categories of endocrines?

1. Hormones

2. Neurohormones

3. Local Hormones

4. Candidate Hormones

What are hormones?

Chemicals released by a gland or cell into the blood stream that affects target cells.

What are neurohormones?

Chemicals released by neurons into the blood stream that affects distant target cells.

What are local hormones?

Chemicals that affect nearby cells via local diffusion.

What are candidate hormones?

Chemicals not universally recognized as hormones, but have at least some attributes of hormones.

What is an antagonistic action? What’s an example of this?

An action where one is opposite of another. An example is insulin and glucagon (with insulin lowering blood sugar level, and glucagon increasing blood sugar level)

What is a permissive action?

An action that requires previous or simultaneous action by another hormone.

What is a synergistic reaction?

A combination of two or more hormones is greater than the sum of the hormones individually.

What are the two types of hormones?

1. Protein (or protein-like) hormones

2. Steroids (or steroid-like) hormones

What are some attributes of a protein (or protein-like) hormone?

extracellular, polar, circulates freely

What are some attributes of a steroid (or steroid-like) hormone?

intracellular, nonpolar, attached to protein (ends in “one” or “gen”)

What are some attributes of an extracellular receptor location?

Usually for lipophobic molecules (mostly proteins).

Tend to have a fast response time.

What are some attributes of an intracellular receptor location?

Can be found in two places.

Tend to be for lipophilic molecules (mostly steroids) who are soluble in the membrane.

Generally affect the rate of protein production. Tend to have a relatively slow response time

What are the two intracellular receptor locations?

1. nuclear (these are typically found on DNA)

2. cytosolic (these are typically found on RNA)

What are the typical second messengers?

• Ca⁺²

• cAMP (cyclic AMP)

• IP₃ (inositol phosphate)

• NO (nitric oxide)

What is the purpose of second messengers?

They cause signal amplification.

Do ligands that bind to extracellular receptors enter the cell?

No! They cause something to happen inside the cell without entering it.

If ligands are molecules activated outside the cell, second messengers are…

molecules that are activated on the interior of the cell.

Another word for ligand?

First messenger

What does the activation of a single ligand (first messenger) cause?

It stimulates second messengers inside the cell which in turn activates a ton of secondary messengers. This is also called amplification!

What are some properties of extracellular receptors (aka protein receptors)?

• Specificity (receptors only bind one class of ligands)

• Competition (ligands compete for binding sites depending on affinity or concentration)

• Saturation (binding sites are limited by open receptor sites)

What are the two ligand subtypes?

1. Agonists - excite or turn on receptor (activators) exciters because they mimic signal molecules

2. Antagonists - block the receptor (inhibitors) and do not allow agonists to excite, thereby slowing down or stopping signal pathway

What is down regulation in terms of receptor turnover? What is an example of this?

A decrease in the number or sensitivity of receptors in response to a high ligand concentration.

Examples of this include drug tolerance and type II diabetes.

What is up regulation in terms of receptor turnover?

An increase in the number or sensitivity of receptors in response to a low ligand concentration.

Why are receptor numbers in a constant flux state?

1. receptors become worn or damaged

2. receptors need to be replaced by new functional receptors

What are the three termination mechanisms for signal pathways?

1. pumping the molecule from the site (calcium pumps)

2. first messenger is degraded by enzymes (AChE)

3. endocytosis of ligand and receptor for destruction

Who came up with the idea of the consistency of the human body's internal environment?

Claude Bernard

Who coined the term “homeostasis” based on four postulates? What were these four postulates?

Walter Canon

1. the autonomic nervous system plays an important role in this process

2. there is always a level of tonic activity

3. there are antagonistic controls

4. chemicals have different effects in different tissues

What are the two categories of homeostasis control?

1. Intrinsic control (aka local control/autoregulation)

2. Extrinsic control (aka distant control)

What are the attributes of intrinsic control?

The organ or system’s control mechanism comes from within itself without outside influence.

• often controlled through the release of autocrines and paracrines

• there may be local electrical communication involved as well

What are the attributes of extrinsic control?

The organ or system’s control mechanism comes from outside that organ or system.

• neural - usually one or both branches of the ANS help control the variable

• humoral - chemically carried in the blood (typically hormones) help control the variable

• other - some other mechanism beside those listed help control the variable

What are the properties of a reflex?

Think GASPI

• G-raded

• A-dequate stimulus

• S-pecific receptor

• P-atterned

• I-nvoluntary

What is the purpose of reflexes?

Reflexes are physiological events that help to control many functions within the human body including homeostasis.

What are the five components involved in a reflex arc?

1. Receptor

2. Sensory fiber (afferent)

3. Integrator (CNS)

4. Motor fiber (efferent)

5. Effector (end organ)

What are sensory receptors in the context of the reflex arc? What are the components of sensory receptors?

Specialized components that detect changes in environment.

• can be central (within CNS), or peripheral

• most have a threshold (minimum stimulus necessary to initiate response)

• some receptors adapt to the stimulus (stimulus has less effect over time)

• some receptors never adapt to the stimulus

What are afferent pathways in the context of the reflex arc? What are the components of afferent pathways?

Also known as the sensory neuron (can be a chemical if it is a hormone).

• it varies according to reflex type

• always carried information towards the integrator

What are integrators in the context of the reflex arc? What are the components of integrators?

A structure that receives information from sensory pathways, analyzes that information and then initiates an output.

• in some cases output is not to change the variable

• other times it can increase or decrease that variable depending on results of integration

What are efferent pathways in the context of the reflex arc? What are the components of efferent pathways?

Also known as the motor neuron (can also be chemical such as a hormone).

• goes from integrating center to effector(s)

• carried information to the end organ to have an effect