Endocrine System #3: Thyroid Gland

Located at the base of the neck, the thyroid gland is one of the biggest endocrine glands in the body.

It's main function is to produce thyroid hormones, which are used for regulating the body's metabolism.

Endocrine System #2: Stress Regulation

The adrenal gland handles stress through secreting various hormones. The adrenal cortex is responsible for dealing with long-term stress, whereas the adrenal medulla is responsible for dealing with short term stress.

Dealing with Short-Term Stress

1. Stress causes the release of the acetylcholine, a neurotransmitter
2. This signals the adrenal cortex to release catecholamines: epinephrine and nor-epinephrine
3. Effects: 1) increased breakdown of glucagon into glucose;  2) increased blood pressure and bloodflow; 3) increased metabolism; 4) decrease in bloodflow to kidneys and intestines, and more blood flows to the brain, muscles and muscles, and 5) increased breathing rate.

Endocrine System #1: Glucose Regulation

In the pancreas, the islets of Langerhans contain cells that secrete hormones that regulate blood glucose levels and glucose metabolism.

The alpha cells secrete glucagon when blood sugar levels are low. Glucagon triggers the liver to break down more glycogen into glucose, and to convert more amino acids and glycerol to glucose.

The beta cells secrete insulin when blood sugar levels are high. Insulin increases cells' glucose uptake by activating their glucose transporters. It also suppresses the liver's ability to convert glycogen to glucose.

Kidney #2— Functions and Mechanisms

1. Blood enters a ball of capillaries called glomerulus
2. Due to high blood pressure (65 mm Hg as opposed to 25 mm Hg), blood is filtered into the lumen of Bowman's capsule. Water and small dissolved molecules (salts, sugar, amino acid, nitrogenous waste, etc.) enter the glomerulus and become the filtrate. Blood cells, plasma proteins, and platelets are filtered out.
•  Bowman's capsule is the blind end of the nephron's tubule, and it surrounds the glomerulus
3. In the proximal tubule, hydrogen ions are secreted, and bicarbonate ions—which are important buffers— are reabsorbed. The epithelial cells also secrete ammonia to maintain a constant pH within the filtrate. In addition, drugs and other toxins are released from the peritubular capillaries, and they travel through the interstitial fluid and are secreted into the filtrate. Furthermore, important nutrients, such as glucose, amino acids, potassium ions, are actively or passively transported back to the blood. Sodium ions are pumped into the interstitial fluid, which allows water to follow by osmosis.
4. The filtrate now travels into the descending limb of the loop of Henle, from the cortex to the inner medulla. In this section, the transport epithelium is permeable to water but not salt and other solutes, so water diffuses out of the tubule.
5. The filtrate now travels up the ascending limb of the loop of Henle, from the inner medulla back to the cortex. In the thin segment that is close to the turn, NaCl is passively diffused out of the tubules, which contributes to the high osmolarity of the inner medulla. In the thick segment in the cortex, NaCl is pumped out of the tubule.
   The reason why an osmotic gradient exists within the entire loop of Henle is that the blood flows in the opposite direction as the filtrate.
6. Next, the filtrate enter the distal tubule. Potassium and hydrogen ions are secreted, and  NaCl and bicarbonate ions are reabsorbed.
7. The filtrate then enters the collecting duct, which carries the filtrate into the renal pelvis (note that the collecting duct collects from several nephrons). Here, sodium chloride is actively transported out of the duct. Also, in the inner medulla, urea diffuses into interstitial fluid. This increases the osmolarity of the interstitial fluid and enables water to be reabsorbed.

Kidney #1

The kidney is an essential organ in the excretory system. It performs the following tasks:

• maintaining blood pressure
• blood filtration
• hormone secretion
• waste excretion
• pH maintenance

Osmoregulation

Osmoregulation is the regulation of body's water content and solute concentration.

Thermoregulation

Physical Adaptations

• Fur, hair, etc to insulate heat

Circulatory Adaption

• Countercurrent flow

Behavioural Adaption

• Gross muscle movements
• huddling
• relocation
• torpor

Physiological Changes

• Regulating rate of heat exchange through vasoconstriction and vasodilation
• Regulating rate of heat production through muscle contractions and shivering
• Regulating rate of metabolic heat production 

DNA Replication-- Summary

The following are the summary of what happens during DNA replication:

1. Starting from the origin of replication (ori), helicase unwinds the the double helix. Single-stranded bonding proteins (SSBPs) bind to the single stranded DNA to keep them apart.
2. RNA polymerase constructs RNA primers on both leading and lagging strands
3. • The leading strand is continuously elongated by DNAP III.
   • The lagging strand is elongated discontinuously. Each okazaki segment is primed with RNAP, and then elongated by by DNAP III. DNAP I replaces the RNA primer with DNA, and DNA ligase joins the fragments together by catalyzing the formation of phosphodiester bonds.
4. This process continues until the replication fork meets the replication fork of another replication bubble, or when the end of the DNA strand is reached.

Plant Technology and Maintanence

Artificial Selection: selecting the desire traits of a plant, and only breed the plants that have the desired traits

• mass selection: selecting the largest and biggest
• pure line selection: selecting certain traits
• cross-breeding: breeding two plants that have two different desired traits

Tissue Culturing Technology

• Obtain cells from the meristem
• Grow the cells through mitosis. The mass of cell is called a callus
• Apply hormones such as auxin and cytokinin so that roots and shoots can grow

Gene transfer: splicing the genes of one species into another to get the desired traits

• Cold resistant gene: obtained from a kind of fish
• Bt gene: codes for proteins that paralyze and kill insects

Common Genetic Disorders

Inherited Disorders:
Autosomal dominant

• Progeria: characterized by rapid aging
• Huntington disease: characterized by involuntary arms and legs movements. Other symptoms include mild irritability and memory loss

Autosomal recessive

• Tay-Sachs Disease:  They lack a certain enzyme that would allow cells to digest lipids. This causes the lipids to build up in the brain cells and destroy, which further causes blindness, mental deterioration, and death
• Phenylketonuria: If untreated, children can be severely mentally handicapped
• Albinism: Lacks the brown pigment melanin

X-linked recessive

• Hemophilia: Reduced ability to clot blood.
• Colour blindness: Cannot distinguish between colours
• Duchenne muscular distrophy: Muscles waste away because the muscle cells are are engorged with fat and connective tissue

Codominance

• Sickle Cell Anemia: RBCs are shaped like sickles, causing reduced blood flow to various parts of the body.

Incomplete Dominance

• Hypercholesterolemia: high cholesterol, so higher chances of heart attack

Aneuploidy (Non disunction):
Down syndrome: trisomy of the 21st chromosome
Edwards syndrome: trisomy of the 13th chromosome
Patau's syndrome: trisomy of the 18th chromosome

Turner's syndrome: only one "x" chromosome
Kinefelter's syndrome: "XXY"
Jacob's syndrome: "XYY"

Common Digestive Diseases

Colon Polyps 
Description/ Symptoms: fleshy growth on the colon. Could cause rectum bleeding and could turn cancerous
Causes: genetic mutations of colon cells
Treatments: Surgeries


Gingivitis 
Description/ Symptoms: inflammation of the gums
Causes: bad oral hygiene, bacteria
Treatments: Better oral hygiene


Diabetes
Description/ Symptoms: not enough insulin; blood sugar too high
Causes: genetic factors, obesity
Treatments: injection of insulin

Quick Review for Plants

Classification

• Plants can be classified as aquatic or terrestrial.
• Of the terrestrial plants, there are ones that are vascular and ones that are non-vascular.
• Of the vascular plants, there are seedless plants, and seed-bearing plants
• Of the seed bearing plants, there are gymnosperms and angiosperms
• Angiosperms can be classified as monocots or dicots

Organs

Leaves

Leaves are primarily responsible for photosynthesis. They are covered by cuticles, which are waxy layers that prevent water loss. They have stomata that allow for plants' gas exchange.

Palisade mesophyll are responsible for photosynthesis.

The Human Respiratory System

As mentioned in the post named Respiration, humans cannot rely on simple diffusion for gas exchange. Instead, we have to rely on a specialized respiratory system to do so.

In this post, I will be describing how the human respiratory system works.   

Nose

The nose (nasal cavity) is where the air comes into our body. The nostrils contain tiny hair that clean the air, and the epithelium lining have capillaries that warm the blood. Also, the turbinate bones are lined with a thin membrane that secrets mucus, which moistens the air.

(turbinate bones: thin bones in the nose that increase surface area, and warm and moisten the air)

Larynx

• The larynx house the vocal cords

Trachea 

• have mucous cells and cilia.
• mucous cells trap foreign particles, and cilia brush them away
• maintains its rigidity because of the cartilage rings

Bronchi

• like the trachea, they are also reinforced with cartilage
• lead to bronchiole, and then alveoli

Alveoli

• Spherical hollow cavities (grape-like structures) that are lined up with capillaries
• where gas exchange occurs

Lung surfactant: a complex substance that reduces the surface tension throughout the lung

Lungs

• The right lung has three lobes, while the left lung has only two lobes (to accommodate for the heart) 
• protected by a flexible membrane called pleura, which allows the lung to expand and contract

Types of respiration:

• Breathing: the act of drawing air into and then out of the lungs
• External respiration: gas exchange between the air and the blood
• Internal respiration: gas exchange between the blood and other cells
• Cellular respiration: the process in which cells convert oxygen and glucose into useful energy, creating carbon dioxide in the process.

Respiration

Cellular respiration: Almost every organism needs cellular respiration, as it allows cells to convert glucose and oxygen into useful energy.

Gas Exchange: As oxygen is a key component in cellular respiration, a cell needs to constantly bring in oxygen so that it can go through cellular respiration. Also, each cell needs to eliminate its carbon dioxide, a waste product of cellular respiration. Therefore, gas exchange— the process by which oxygen enters a cell and carbon dioxide leaves it— is necessary.

Requirements for gas exhange:

• large surface area: so that it can occur at a fast-enough speed
• moist environment

Diffusion

• Diffusion is a natural process in which molecules travel from areas of high concentration to low concentration
• It is only effective if an organism is only a few cells think
• Therefore, only uni-cellular organisms and very thin multi-cellular organisms (such as planarian) rely on diffusion

Specialized Respiratory Systems

• As organisms become larger, diffusion becomes inefficient.
• Also, many cells become specialized for other functions (e.g., reproduction)
• Therefore, a respiratory system is needed — a system that consists of respiratory surfaces, and muscles and tubes that allow air to contact the surface.
• Different types:
• Skin Respiration: The skin is lined with capillaries so that air can diffuse from the skin into the blood. The blood then transfers the oxygen to rest of the organism. Since diffusion must occur in a moist environment, organisms that rely on skin respiration must live in moist/damp environments. Examples: annelids (including earthworms, leeches)
• Gills: gills are organs that have high surface area and a lot of capillaries. They allow diffusion and gas exchange to occur efficiently for aquatic animals. 
• Tracheal Respiratory System: This is for insects. Many insects have spiracles (external pores) that allow the air to go into their trachea, which come in close contact to all the living cells.
• Lungs: organs that forcibly bring in air so that gas exchange can occur at the capillaries located on the lung surface. The blood then transports the oxygen to other parts of the body.

Digestive Tract #2

This is a continuation of Digestive Tract #1.


Small Intestines:

After turning into chyme, the food enters the small intestines, which are comprised of three parts:

• Duodenum: receives secretions from the gall bladder and the pancreas (pancreatic juice). It is where the majority of chemical digestion takes place
• Jejunum: absorption of carbohydrates and proteins takes place
• Ileum: absorption takes place, especially vitamin B-12 and bile salts

Large Intestines:
The large intestines absorb water, and they also contain bacteria that produce vitamin K and vitamin B-12. In addition, they pass waste material to the anus.

Anus:
The anus expels the wastes.

Pancreas:
The pancreas secretes bicarbonate ions, which neutralize the stomach acid and inactivates pepsin. The pancreas also secretes pancreatic juice, which is comprised of pancreatic amylase (breaks down starch), lipase and trypsin.

Gall Bladder:
The gall bladder stores bile, which emulsifies fat and allows a greater surface area for fat to be broken down .

Liver:
The liver produces bile and cholesterol. It also converts excess glucose to glycogen, detoxifies poisons, and stores fat-soluble vitamins.

Digestive Tract #1

The digestive tract (also called the alimentary canal or the gastrointestineal tract) consists of: mouth→ pharynx→ epiglottis→ esophagus→ stomach→ small intestine→ large intestine→ anus

This entire post will be used to describe each part of the digestive tract, as well as other organs in the digestive system, such as livers and gallbladders.

Mouth:
The mouth (oral cavity) is where the food enters our body, and in it, both physical and chemical digestion take place.

The teeth physically break down the food, with different types of teeth breaking the food down different ways:

The saliva contains mucus and enzymes, such as amylase (breaks down polysaccharides) and maltase. Saliva is produced by the salivary glands, which are the parotid gland, the sublingual gland, and the submandibular gland:

The tongue moves the food when the person is chewing. In addition, it has taste buds, which are receptors that send messages to our brain: 

In the mouth, with the chewing and the mixing with the saliva, the food becomes a food bolus, and it now travels to the pharynx.

Esophagus: 

The food bolus then goes through the pharynx and into the esophagus, and long muscular tube made up circular and longitudinal muscles. In the esophagus, food is moved along with peristalsis.

Stomach:
At the end of the esophagus, there's the cardiac sphincter, which controls the movement of the food from the esophagus to the stomach. The stomach is a J-shaped organ with a volume of 1.5L, and it has thick layers of smooth muscle (rugae) that allows it to stretch. The stomach uses its longitudinal, circular, and oblique muscles to churn the food, and it also secretes gastric juices to chemically digest the food.

With both physical and chemical digestion, the food bolus is turned into a thick liquid called chyme.

Some components of the gastric juice:

• Hydrochloric acid: destroys invading microbes, breaks down food bolus, and turns pepsinogen into pepsin
• Pepsinogen: In acidic environments, it turns into pepsin, which breaks polypeptides into dipeptides
• Lipases: enzymes that break down lipids
• Mucus: secreted by the rugae, it forms a protective coating for the stomach that prevents the hydrochloric acid from burning through

Essential Nutrients

Nutrients are chemicals that an organism needs to carry out its life processes.

Out of all the nutrients, many of them need be obtained from our diet. This may be because our bodies do not synthesize enough of these nutrients, or because our bodies do not synthesize thems at all. We call these nutrients essential nutrients, and categorize them into the following: carbohydrates, fats, proteins, minerals, vitamins, and water.

Early Ideas/Beliefs About Heredity

Hippocrates:
Greek philosopher Hippocrates believed that every part of the parents produced "seeds," which would fuse together to create the offspring

Aristotle:
Aristotle believed that male and female semen mixed upon conception.

George Harvey
English physician George Harvey theorized that individuals arose through the process of epigenesis; he believed that embryos formed in stages and that their development could be affected by factors inside and outside of the mother.  

Anton van Leeuwenhoek
This dutch scientist, who invented the microscope, believed that each sperm contained preformed embryos and that the development of the offspring was controlled by the male parent. On the other hand, mothers had almost no effect on the offspring, except providing an environment for the embroys to develop.

Charles Darwin
Charles Darwin believed that the offspring contained variations of traits from both parents. However, he couldn't explain why.

Pangenesis
The belief that each organ contains "genes," which travel through blood, the parents' genitals, and into the children.

Blending Traits:
The belief that offsprings are the "mix" of the parents. (e,g, red flowers and blue flowers would produce purple flowers)

Life Cycle

Fertilization:

• Male and female gametes (egg and sperm) combine to form a zygote. 
• Gonads are organs that produce gametes (male: testes, female: ovaries)

Incubation

• Embryos→ fetus→ infant
• growth through cell division and differenciation

Growth

• Cell division of somatic cells (non-sex cells).  

Reproduction

• Puberty: parts of body begin to be able to make sex cells
• Meiosis: make more gametes

The Cell Cycle

Interphase

• G1: The cell grows and duplicates its contents (except the chromosomes).
• S: The cell duplicates its chromosomes
• G2: The cell checks for error in the duplicated chromosomes

Mitosis

• Prophase: the cell's chromosomes become visible, and nuclear membranes begin to dissolve. Also, centrioles migrate to opposite poles of the cell, and spindle fibres begin to form between the two centrioles.
• Metaphase: The chromotids move to the center of the cell, and form the metaphase plate.
• Anaphase: The centromere splits apart, and the chromotids move to the opposing poles of the cell.
• Telophase: nuclear membrane begins to reappear. Chromosomes begin to uncoil. The spindle fibres begin to disappear

Cytokinesis: 

- The two daughter cells separate